Make it more clear that a positional pattern relies on Deconstruct (dotnet#42514)

* Make it more clear that a positional pattern relies on `Deconstruct`

 Fixes dotnet#42307

* Update docs/csharp/language-reference/operators/patterns.md

Co-authored-by: Genevieve Warren <[email protected]>

---------

Co-authored-by: Genevieve Warren <[email protected]>

Author: BillWagner

docs/csharp/language-reference/operators/patterns.md

@@ -195,7 +195,12 @@ You use a *positional pattern* to deconstruct an expression result and match the
 
 :::code language="csharp" source="snippets/patterns/PositionalPattern.cs" id="BasicExample":::
 
-At the preceding example, the type of an expression contains the [Deconstruct](../../fundamentals/functional/deconstruct.md) method, which is used to deconstruct an expression result. You can also match expressions of [tuple types](../builtin-types/value-tuples.md) against positional patterns. In that way, you can match multiple inputs against various patterns, as the following example shows:
+At the preceding example, the type of an expression contains the [Deconstruct](../../fundamentals/functional/deconstruct.md) method, which is used to deconstruct an expression result.
+
+>[!IMPORTANT]
+> The order of members in a positional pattern must match the order of parameters in the `Deconstruct` method. That's because the code generated for the positional pattern calls the `Deconstruct` method.
+
+You can also match expressions of [tuple types](../builtin-types/value-tuples.md) against positional patterns. In that way, you can match multiple inputs against various patterns, as the following example shows:
 
 :::code language="csharp" source="snippets/patterns/PositionalPattern.cs" id="MatchTuple":::