diff --git a/xml/System/AggregateException.xml b/xml/System/AggregateException.xml
index ab49f6f501d..a88ecc20d27 100644
--- a/xml/System/AggregateException.xml
+++ b/xml/System/AggregateException.xml
@@ -728,8 +728,8 @@
         <ReturnType>System.String</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets a message that describes the exception.</summary>
+        <value>The message that describes the exception.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -772,4 +772,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/Double.xml b/xml/System/Double.xml
index a00dc3e4d33..05906245c8e 100644
--- a/xml/System/Double.xml
+++ b/xml/System/Double.xml
@@ -850,9 +850,9 @@
         <Parameter Name="d" Type="System.Double" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="d">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="d">A double-precision floating-point number.</param>
+        <summary>Determines whether the specified value is finite (zero, subnormal, or normal).</summary>
+        <returns><see langword="true" /> if the value is finite (zero, subnormal or normal); <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1021,9 +1021,9 @@
         <Parameter Name="d" Type="System.Double" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="d">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="d">A double-precision floating-point number.</param>
+        <summary>Determines whether the specified value is negative.</summary>
+        <returns><see langword="true" /> if the value is negative; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1122,9 +1122,9 @@
         <Parameter Name="d" Type="System.Double" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="d">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="d">A double-precision floating-point number.</param>
+        <summary>Determines whether the specified value is normal.</summary>
+        <returns><see langword="true" /> if the value is normal; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1217,9 +1217,9 @@
         <Parameter Name="d" Type="System.Double" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="d">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="d">A double-precision floating-point number.</param>
+        <summary>Determines whether the specified value is subnormal.</summary>
+        <returns><see langword="true" /> if the value is subnormal; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -3915,4 +3915,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/Environment.xml b/xml/System/Environment.xml
index 158a5732124..17db957142c 100644
--- a/xml/System/Environment.xml
+++ b/xml/System/Environment.xml
@@ -2085,8 +2085,8 @@ The following example creates environment variables for the <xref:System.Environ
         <ReturnType>System.Int64</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets the number of milliseconds elapsed since the system started.</summary>
+        <value>The elapsed milliseconds since the system started.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
diff --git a/xml/System/FormattableString.xml b/xml/System/FormattableString.xml
index 6166d0c9953..aaa6dc4c1ad 100644
--- a/xml/System/FormattableString.xml
+++ b/xml/System/FormattableString.xml
@@ -142,10 +142,28 @@
         <Parameter Name="formattable" Type="System.FormattableString" Index="0" FrameworkAlternate="netcore-3.0" />
       </Parameters>
       <Docs>
-        <param name="formattable">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <param name="formattable">The string to be formatted.</param>
+        <summary>Returns a result string in which arguments are formatted by using the conventions of the current culture.</summary>
+        <returns>The string that results from formatting the current instance by using the conventions of the current culture.</returns>
+        <remarks>
+          <format type="text/markdown">
+  <![CDATA[
+
+### Remarks
+
+This static method may be imported in C# by:
+
+```csharp
+    using static System.FormattableString;
+```
+
+Within the scope of that import directive, an interpolated string may be formatted in the current culture by writing, for example:
+
+```csharp
+    CurrentCulture($"{{ lat = {latitude}; lon = {longitude} }}");
+```
+
+          ]]></format>.</remarks>
       </Docs>
     </Member>
     <Member MemberName="Format">
@@ -468,4 +486,4 @@ Invariant($"{{ lat = {latitude}; lon = {longitude} }}")
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/Index.xml b/xml/System/Index.xml
index 2968eeb9308..1f9e6ddb058 100644
--- a/xml/System/Index.xml
+++ b/xml/System/Index.xml
@@ -27,8 +27,21 @@
     </Attribute>
   </Attributes>
   <Docs>
-    <summary>To be added.</summary>
-    <remarks>To be added.</remarks>
+    <summary>Represent a type can be used to index a collection either from the start or the end.</summary>
+    <remarks>
+      <format type="text/markdown"><![CDATA[
+
+### Remarks
+
+`Index` is used by the C# compiler to support the new index syntax:
+
+```csharp
+    int[] someArray = new int[5] { 1, 2, 3, 4, 5 };
+    int lastElement = someArray[^1]; // lastElement = 5
+```
+
+          ]]></format>
+    </remarks>
   </Docs>
   <Members>
     <Member MemberName=".ctor">
@@ -52,10 +65,20 @@
         <Parameter Name="fromEnd" Type="System.Boolean" />
       </Parameters>
       <Docs>
-        <param name="value">To be added.</param>
-        <param name="fromEnd">To be added.</param>
-        <summary>To be added.</summary>
-        <remarks>To be added.</remarks>
+        <param name="value">The index value. It has to be greater or equal than zero.</param>
+        <param name="fromEnd">A boolean indicating if the index is from the start (<see langword="false" />) or from the end (<see langword="true" />) of a collection.</param>
+        <summary>Initializes a new <see cref="T:System.Index" /> with a specified index position and a value that indicates if the index is from the start or the end of a collection.</summary>
+        <remarks>
+          <format type="text/markdown">
+            <![CDATA[
+
+### Remarks
+
+If the <see cref="T:System.Index" /> is constructed from the end, an index value of 1 points to the last element, and an index value of 0 points beyond last element.
+
+            ]]>
+          </format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="End">
@@ -78,8 +101,8 @@
         <ReturnType>System.Index</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets an <see cref="T:System.Index" /> that points beyond the last element.</summary>
+        <value>an <see cref="T:System.Index" /> that points beyond the last element.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -109,9 +132,9 @@
         <Parameter Name="other" Type="System.Index" />
       </Parameters>
       <Docs>
-        <param name="other">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="other">The object to compare with this instance.</param>
+        <summary>Returns a value that indicates whether the current object is equal to another <see cref="T:System.Index" /> object.</summary>
+        <returns><see langword="true" /> if the current Index object is equal to <paramref name="other" />; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -138,9 +161,9 @@
         <Parameter Name="value" Type="System.Object" />
       </Parameters>
       <Docs>
-        <param name="value">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="value">An object to compare with this instance.</param>
+        <summary>Indicates whether the current Index object is equal to a specified object.</summary>
+        <returns><see langword="true" /> if <paramref name="value" /> is of type <see cref="T:System.Index" /> and is equal to the current instance; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -167,9 +190,9 @@
         <Parameter Name="value" Type="System.Int32" />
       </Parameters>
       <Docs>
-        <param name="value">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="value">The index value from the end of a collection.</param>
+        <summary>Creates an <see cref="T:System.Index" /> from the end of a collection at a specified index position.</summary>
+        <returns>The Index value.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -196,9 +219,9 @@
         <Parameter Name="value" Type="System.Int32" />
       </Parameters>
       <Docs>
-        <param name="value">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="value">The index position from the start of a collection.</param>
+        <summary>Create an <see cref="T:System.Index" /> from the specified index at the start of a collection.</summary>
+        <returns>The index value.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -223,8 +246,8 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <summary>Returns the hash code for this instance.</summary>
+        <returns>The hash code.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -251,10 +274,22 @@
         <Parameter Name="length" Type="System.Int32" />
       </Parameters>
       <Docs>
-        <param name="length">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <param name="length">The length of the collection that the Index will be used with. Must be a positive value.</param>
+        <summary>Calculates the offset from the start using the given collection length.</summary>
+        <returns>The offset.</returns>
+        <remarks>
+          <format type="text/markdown">
+            <![CDATA[
+
+## Remarks
+
+For performance reasons, this method does not validate if `length` or the returned value are negative. It also doesn't validate if the returned value is greater than `length`.
+
+Collections are not expected to have a non-negative length/count. If this method's returned offset is negative and is then used to index a collection, the runtime will throw <xref:System.ArgumentOutOfRangeException>, which will have the same effect as validation.
+
+          ]]>
+          </format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="IsFromEnd">
@@ -277,8 +312,8 @@
         <ReturnType>System.Boolean</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets a value that indicates whether the index is from the start or the end.</summary>
+        <value><see langword="true" /> if the Index is from the end; otherwise, <see. langword="false" />.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -305,9 +340,9 @@
         <Parameter Name="value" Type="System.Int32" />
       </Parameters>
       <Docs>
-        <param name="value">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="value">The integer to convert.</param>
+        <summary>Converts integer number to an Index.</summary>
+        <returns>An Index representing the integer.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -331,8 +366,8 @@
         <ReturnType>System.Index</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets an <see cref="T:System.Index" /> that points to the first element of a collection.</summary>
+        <value>An instance that points to the first element of a collection.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -357,8 +392,8 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <summary>Returns the string representation of the current <see cref="T:System.Index" /> instance.</summary>
+        <returns>The string representation of the <see cref="T:System.Index" />.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -382,10 +417,10 @@
         <ReturnType>System.Int32</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets the index value.</summary>
+        <value>The index value.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/Progress`1.xml b/xml/System/Progress`1.xml
index 939cf37d096..3d2de3286ee 100644
--- a/xml/System/Progress`1.xml
+++ b/xml/System/Progress`1.xml
@@ -125,6 +125,7 @@
         <param name="handler">A handler to invoke for each reported progress value. This handler will be invoked in addition to any delegates registered with the <see cref="E:System.Progress`1.ProgressChanged" /> event. Depending on the <see cref="T:System.Threading.SynchronizationContext" /> instance captured by the <see cref="T:System.Progress`1" /> at construction, it is possible that this handler instance could be invoked concurrently with itself.</param>
         <summary>Initializes the <see cref="T:System.Progress`1" /> object with the specified callback.</summary>
         <remarks>To be added.</remarks>
+        <exception cref="T:System.ArgumentNullException"><paramref name="handler" /> is <see langword="null" /> (<see langword="Nothing" /> in Visual Basic).</exception>
       </Docs>
     </Member>
     <Member MemberName="OnReport">
@@ -247,4 +248,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/Range.xml b/xml/System/Range.xml
index bcec175b323..e85993a001f 100644
--- a/xml/System/Range.xml
+++ b/xml/System/Range.xml
@@ -27,8 +27,24 @@
     </Attribute>
   </Attributes>
   <Docs>
-    <summary>To be added.</summary>
-    <remarks>To be added.</remarks>
+    <summary>Represents a range that has start and end indexes.</summary>
+    <remarks>
+      <format type="text/markdown">
+        <![CDATA[
+
+### Remarks
+
+`Range` is used by the C# compiler to support the range syntax:
+
+```csharp
+    int[] someArray = new int[5] { 1, 2, 3, 4, 5 };
+    int[] subArray1 = someArray[0..2];               // { 1, 2 }
+    int[] subArray2 = someArray[1..^0];              // { 2, 3, 4, 5 }
+```
+
+          ]]>
+      </format>
+    </remarks>
   </Docs>
   <Members>
     <Member MemberName=".ctor">
@@ -52,9 +68,9 @@
         <Parameter Name="end" Type="System.Index" />
       </Parameters>
       <Docs>
-        <param name="start">To be added.</param>
-        <param name="end">To be added.</param>
-        <summary>To be added.</summary>
+        <param name="start">The inclusive start index of the range.</param>
+        <param name="end">The exclusive end index of the range.</param>
+        <summary>Instantiates a new <see cref="T:System.Range" /> instance with the specified starting and ending indexes.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -78,8 +94,8 @@
         <ReturnType>System.Range</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets a <see cref="T:System.Range" /> object that starts from the first element to the end.</summary>
+        <value>A range from the start to the end.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -103,8 +119,8 @@
         <ReturnType>System.Index</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets an <see cref="T:System.Index" /> that represents the exclusive end index of the range.</summary>
+        <value>The end index of the range.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -131,9 +147,9 @@
         <Parameter Name="end" Type="System.Index" />
       </Parameters>
       <Docs>
-        <param name="end">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="end">The position of the last element up to which the <see cref="T:System.Range" /> object will be created.</param>
+        <summary>Creates a <see cref="T:System.Range" /> object starting from the first element in the collection to a specified end index.</summary>
+        <returns>A range that starts from the first element to <paramref name="end" />.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -160,9 +176,9 @@
         <Parameter Name="value" Type="System.Object" />
       </Parameters>
       <Docs>
-        <param name="value">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="value">An object to compare with this Range object.</param>
+        <summary>Returns a value that indicates whether the current instance is equal to a specified object.</summary>
+        <returns><see langword="true" /> if <paramref name="value" /> is of type <see cref="T:System.Range" /> and is equal to the current instance; otherwise, <see langword="false" />.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -192,9 +208,9 @@
         <Parameter Name="other" Type="System.Range" />
       </Parameters>
       <Docs>
-        <param name="other">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="other">A Range object to compare with this Range object.</param>
+        <summary>Returns a value that indicates whether the current instance is equal to another <see cref="T:System.Range" /> object.</summary>
+        <returns><see langword="true" /> if the current instance is equal to <paramref name="other" />; otherwise, <see langword="false" />.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -219,8 +235,8 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <summary>Returns the hash code for this instance.</summary>
+        <returns>The hash code.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -247,10 +263,21 @@
         <Parameter Name="length" Type="System.Int32" Index="0" FrameworkAlternate="netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="length">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <param name="length">A positive integer that represents the length of the collection that the range will be used with.</param>
+        <summary>Returns a <see cref="T:System.Range.OffsetAndLength" /> instance with the starting offset and length of a range.</summary>
+        <returns>The starting offset and length of the range.</returns>
+        <remarks>
+          <format type="text/markdown">
+            <![CDATA[
+
+## Remarks
+
+For performance reasons, this method does't validate `length` to ensure that it is not negative. It does ensure that `length` is within the current `Range` instance. 
+
+            ]]>
+          </format>
+        </remarks>
+        <exception cref="T:System.ArgumentOutOfRangeException"><paramref name="length" /> is outside the bounds of the current range. </exception>
       </Docs>
     </Member>
     <Member MemberName="Start">
@@ -273,8 +300,8 @@
         <ReturnType>System.Index</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>To be added.</summary>
-        <value>To be added.</value>
+        <summary>Gets the inclusive start index of the <see cref="T:System.Range" />.</summary>
+        <value>The inclusive start index of the range.</value>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -301,9 +328,9 @@
         <Parameter Name="start" Type="System.Index" />
       </Parameters>
       <Docs>
-        <param name="start">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="start">The position of the first element from which the Range will be created.</param>
+        <summary>Returns a new <see cref="T:System.Range" /> instance starting from a specified start index to the end of the collection.</summary>
+        <returns>A range from <paramref name="start" /> to the end of the collection.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -328,10 +355,10 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <summary>Returns the string representation of the current <see cref="T:System.Range" /> object.</summary>
+        <returns>The string representation of the range.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/ReadOnlySpan`1.xml b/xml/System/ReadOnlySpan`1.xml
index 22f7dbc68b3..56950a4b5f7 100644
--- a/xml/System/ReadOnlySpan`1.xml
+++ b/xml/System/ReadOnlySpan`1.xml
@@ -144,7 +144,17 @@ A `ReadOnlySpan<T>` instance is often used to reference the elements of an array
         <param name="start">The index of the first element to include.</param>
         <param name="length">The number of elements to include.</param>
         <summary>Creates a new <see cref="T:System.ReadOnlySpan`1" /> that includes a specified number of elements of an array starting at a specified index.</summary>
-        <remarks>To be added.</remarks>
+        <remarks>
+          <format type="text/markdown">
+            <![CDATA[
+
+### Remarks
+
+This method returns `default` when `array` is `null`.
+
+            ]]>
+          </format>
+        </remarks>
         <exception cref="T:System.ArgumentOutOfRangeException">
           <paramref name="array" /> is <see langword="null" />, but <paramref name="start" /> or <paramref name="length" /> is non-zero.
 
@@ -888,4 +898,4 @@ If the `destination` length is shorter than `source`, no items are copied and th
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/SequencePosition.xml b/xml/System/SequencePosition.xml
index 9e1e1ae7e8c..6618e9ceb38 100644
--- a/xml/System/SequencePosition.xml
+++ b/xml/System/SequencePosition.xml
@@ -29,7 +29,7 @@
     </Attribute>
   </Attributes>
   <Docs>
-    <summary>Represents position in a non-contiguous set of memory. Properties of this type shouldn't be interpreted by anything but the type that created it.</summary>
+    <summary>Represents a position in a non-contiguous set of memory. Properties of this type should not be interpreted by anything but the type that created it.</summary>
     <remarks>To be added.</remarks>
   </Docs>
   <Members>
@@ -55,8 +55,8 @@
         <Parameter Name="integer" Type="System.Int32" />
       </Parameters>
       <Docs>
-        <param name="object">To be added.</param>
-        <param name="integer">To be added.</param>
+        <param name="object">A non-contiguous set of memory.</param>
+        <param name="integer">The position in <paramref name="object" />.</param>
         <summary>Initializes a new instance of the <see cref="T:System.SequencePosition" /> struct.</summary>
         <remarks>To be added.</remarks>
       </Docs>
@@ -91,10 +91,18 @@
         <Parameter Name="obj" Type="System.Object" />
       </Parameters>
       <Docs>
-        <param name="obj">An object to compare to this instance.</param>
-        <summary>Returns a value that indicates whether this instance is equal to the specified object. <see cref="T:System.SequencePosition" /> equality does not guarantee that they point to the same location in <see cref="T:System.Buffers.ReadOnlySequence`1" />.</summary>
-        <returns><see langword="true" /> if <paramref name="obj" /> is an instance of <see cref="T:System.SequencePosition" /> and has the same value as this instance; otherwise, <see langword="false" />.</returns>
-        <remarks>To be added.</remarks>
+        <param name="obj">The object to compare with the current instance.</param>
+        <summary>Returns a value that indicates whether the current instance is equal to another object.</summary>
+        <returns><see langword="true" /> if <paramref name="obj" /> is of type <see cref="T:System.SequencePosition" /> and is equal to the current instance; otherwise, <see langword="false" />.</returns>
+        <remarks>
+          <format type="text/markdown"><![CDATA[
+          
+## Remarks
+
+Equality does not guarantee that the two instances point to the same location in a <xref:System.Buffers.ReadOnlySequence`1>.
+
+          ]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="Equals">
@@ -125,10 +133,19 @@
         <Parameter Name="other" Type="System.SequencePosition" />
       </Parameters>
       <Docs>
-        <param name="other">The sequence position to compare with this instance.</param>
-        <summary>Returns a value indicating whether this instance is equal to the specified sequence position. <see cref="T:System.SequencePosition" /> equality does not guarantee that they point to the same location in <see cref="T:System.Buffers.ReadOnlySequence`1" />.</summary>
-        <returns><see langword="true" /> if <paramref name="obj" /> has the same value as this instance; otherwise, <see langword="false" />.</returns>
-        <remarks>To be added.</remarks>
+        <param name="other">The sequence position to compare with the current instance.</param>
+        <summary>Indicates whether the current instance is equal to another <see cref="T:System.SequencePosition" />.</summary>
+        <returns><see langword="true" /> if the two instances are equal; <see langword="false" /> otherwise.</returns>
+        <remarks>
+          <format type="text/markdown"><![CDATA[
+          
+## Remarks
+
+Equality does not guarantee that the two instances point to the same location in a <xref:System.Buffers.ReadOnlySequence`1>.
+
+          ]]>
+          </format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="GetHashCode">
@@ -159,8 +176,8 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <summary>Returns the hash code for this instance.</summary>
+        <returns>The hash code for this instance.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -193,7 +210,7 @@
       <Parameters />
       <Docs>
         <summary>Returns the integer part of this <see cref="T:System.SequencePosition" />.</summary>
-        <returns>The integer part of this <see cref="T:System.SequencePosition" />.</returns>
+        <returns>The integer part of this sequence position.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -226,7 +243,7 @@
       <Parameters />
       <Docs>
         <summary>Returns the object part of this <see cref="T:System.SequencePosition" />.</summary>
-        <returns>The object part of this <see cref="T:System.SequencePosition" />.</returns>
+        <returns>The object part of this sequence position.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
diff --git a/xml/System/Single.xml b/xml/System/Single.xml
index 7556dadea11..1e76f4c3b89 100644
--- a/xml/System/Single.xml
+++ b/xml/System/Single.xml
@@ -862,9 +862,9 @@
         <Parameter Name="f" Type="System.Single" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="f">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="f">A single-precision floating-point number.</param>
+        <summary>Determines whether the specified value is finite (zero, subnormal or normal).</summary>
+        <returns><see langword="true" /> if the specified value is finite (zero, subnormal or normal); otherwise, <see langword="false" />.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1033,9 +1033,9 @@
         <Parameter Name="f" Type="System.Single" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="f">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="f">A single-precision floating-point number.</param>
+        <summary>Determines whether the specified value is negative.</summary>
+        <returns><see langword="true" /> if negative, <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1133,9 +1133,9 @@
         <Parameter Name="f" Type="System.Single" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="f">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="f">A single-precision floating-point number.</param>
+        <summary>Determines whether the specified value is normal.</summary>
+        <returns><see langword="true" /> if <paramref name="f" /> is normal; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1233,9 +1233,9 @@
         <Parameter Name="f" Type="System.Single" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="f">To be added.</param>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <param name="f">A single-precision floating-point number.</param>
+        <summary>Determines whether the specified value is subnormal.</summary>
+        <returns><see langword="true" /> if <paramref name="f" /> is subnormal; <see langword="false" /> otherwise.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -3914,4 +3914,4 @@
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/Span`1.xml b/xml/System/Span`1.xml
index 24f9ff9f7cf..5cdc0bdd9eb 100644
--- a/xml/System/Span`1.xml
+++ b/xml/System/Span`1.xml
@@ -200,7 +200,17 @@ If `array` is `null`, this constructor returns a `null` `Span<T>`.
         <param name="start">The index of the first element to include in the new <see cref="T:System.Span`1" />.</param>
         <param name="length">The number of elements to include in the new <see cref="T:System.Span`1" />. </param>
         <summary>Creates a new <see cref="T:System.Span`1" /> object that includes a specified number of elements of an array starting at a specified index.</summary>
-        <remarks>To be added.</remarks>
+        <remarks>
+          <format type="text/markdown">
+            <![CDATA[
+
+### Remarks
+
+This method returns `default` when `array` is `null`.
+
+            ]]>
+          </format>
+        </remarks>
         <exception cref="T:System.ArgumentOutOfRangeException">
           <paramref name="array" /> is <see langword="null" />, but <paramref name="start" /> or <paramref name="length" /> is non-zero.
 
diff --git a/xml/System/String.xml b/xml/System/String.xml
index 85efebb00e0..9034900baba 100644
--- a/xml/System/String.xml
+++ b/xml/System/String.xml
@@ -4762,9 +4762,19 @@ Depending on Why you want to call the `Copy` method, there are a number of alter
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
-        <remarks>To be added.</remarks>
+        <summary>Returns an enumeration of <see cref="T:System.Text.Rune" /> from this string.</summary>
+        <returns>A string rune enumerator.</returns>
+        <remarks>
+          <format type="text/markdown">
+            <![CDATA[
+
+### Remarks
+
+Invalid sequences are represented in the enumeration by <xref:System.Text.Rune.ReplacementChar?displayProperty=nameWithType>.
+
+            ]]>
+          </format>
+        </remarks>
       </Docs>
     </Member>
     <MemberGroup MemberName="Equals">
@@ -6413,9 +6423,10 @@ String 'This is a string.' in domain 'NewDomain': 75CC8236
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <summary>Returns a reference to the first element of the string.</summary>
+        <returns>A pinnable reference to the first element of the string as a read-only char.</returns>
         <remarks>To be added.</remarks>
+        <exception cref="T:System.NullReferenceException">The string is <see langword="null" />.</exception>
       </Docs>
     </Member>
     <Member MemberName="GetTypeCode">
diff --git a/xml/System/ValueTuple.xml b/xml/System/ValueTuple.xml
index f234c04c44b..9126a3dca32 100644
--- a/xml/System/ValueTuple.xml
+++ b/xml/System/ValueTuple.xml
@@ -1124,8 +1124,18 @@ The <xref:System.ValueTuple> type is not serializable in .NET Core 1.x or in the
       <Docs>
         <summary>Returns the string representation of this <see cref="T:System.ValueTuple" /> instance.</summary>
         <returns>This method always returns "()".</returns>
-        <remarks>To be added.</remarks>
+        <remarks>
+          <format type="text/markdown">
+            <![CDATA[
+
+## Remarks
+
+The string returned by this method takes the form `()`.
+
+            ]]>
+          </format>
+        </remarks>
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>
diff --git a/xml/System/ValueTuple`2.xml b/xml/System/ValueTuple`2.xml
index 30f00d1b2e2..2e3546845c0 100644
--- a/xml/System/ValueTuple`2.xml
+++ b/xml/System/ValueTuple`2.xml
@@ -513,7 +513,19 @@ The <xref:System.ValueTuple%602> type is not serializable in .NET Core 1.x or in
         <summary>Returns a value that indicates whether the current <see cref="T:System.ValueTuple`2" /> instance is equal to a specified object based on a specified comparison method.</summary>
         <returns>
           <see langword="true" /> if the current instance is equal to the specified objects; otherwise, <see langword="false" />.</returns>
-        <remarks>To be added.</remarks>
+        <remarks>
+          <format type="text/markdown">
+            <![CDATA[
+
+### Remarks
+
+This member is an explicit interface member implementation. It can be used only when the <xref:System.ValueTuple`2> instance is cast to an <xref:System.Collections.IStructuralEquatable> interface.
+            
+The <xref:System.Collections.IEqualityComparer.Equals(System.Object,System.Object)?displayProperty=nameWithType> implementation is called only if `other` is not `null`, and if it can be successfully cast to a <xref:System.ValueTuple`2> whose components are of the same types as those of the current instance. The <xref:System.Collections.IStructuralEquatable.Equals(System.Object,System.Collections.IEqualityComparer)?displayProperty=nameWithType> method first passes the <xref:System.ValueTuple`2.Item1> values of the <xref:System.ValueTuple`2> objects to be compared to the <xref:System.Collections.IEqualityComparer.Equals(System.Object,System.Object)> implementation. If this method call returns `true`, the method is called again and passed the <xref:System.ValueTuple`2.Item2> values of the two <xref:System.ValueTuple`2> instances.
+
+            ]]>
+          </format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="System.Collections.IStructuralEquatable.GetHashCode">
@@ -755,4 +767,4 @@ The <xref:System.ValueTuple%602> type is not serializable in .NET Core 1.x or in
       </Docs>
     </Member>
   </Members>
-</Type>
\ No newline at end of file
+</Type>