Add documentation for wildcard pattern's ability to match nothing

Co-authored-by: BillWagner <[email protected]>

Author: Copilot

docs/fsharp/language-reference/pattern-matching.md

@@ -172,7 +172,17 @@ The record pattern is used to decompose records to extract the values of fields.
 
 ## Wildcard Pattern
 
-The wildcard pattern is represented by the underscore (`_`) character and matches any input, just like the variable pattern, except that the input is discarded instead of assigned to a variable. The wildcard pattern is often used within other patterns as a placeholder for values that are not needed in the expression to the right of the `->` symbol. The wildcard pattern is also frequently used at the end of a list of patterns to match any unmatched input. The wildcard pattern is demonstrated in many code examples in this topic. See the preceding code for one example.
+The wildcard pattern is represented by the underscore (`_`) character and matches any input, just like the variable pattern, except that the input is discarded instead of assigned to a variable. The wildcard pattern is often used within other patterns as a placeholder for values that are not needed in the expression to the right of the `->` symbol. The wildcard pattern is also frequently used at the end of a list of patterns to match any unmatched input.
+
+In addition to matching any input, the wildcard pattern can effectively match "nothing" in certain contexts:
+
+- When used in function parameters, it ignores the arguments entirely, treating them as if they were not there.
+- When matching the unit type `()`, which represents the absence of a meaningful value.
+- When destructuring data structures, it ignores specific elements that are not needed.
+
+[!code-fsharp[Main](~/samples/snippets/fsharp/lang-ref-2/snippet4818.fs)]
+
+The wildcard pattern is demonstrated in many code examples in this topic. See the preceding code for one example.
 
 ## Patterns That Have Type Annotations
 

samples/snippets/fsharp/lang-ref-2/snippet4818.fs

@@ -0,0 +1,25 @@
+// Wildcard pattern matching "nothing" examples
+open System
+
+// Example 1: Wildcard matching unit type (representing nothing)
+let processUnit x =
+    match x with
+    | () -> "Matched unit (nothing)"
+
+// Example 2: Wildcard ignoring function parameters
+let ignoreAllParams _ _ = "Ignores all input"
+
+// Example 3: Wildcard in destructuring, ignoring elements
+let getFirstOnly (first, _) = first
+
+// Example 4: Using wildcard to ignore optional values
+let handleEmpty opt =
+    match opt with
+    | Some _ -> "Has something"
+    | None -> "Has nothing"
+
+// Usage
+printfn "%s" (processUnit ())
+printfn "%s" (ignoreAllParams 42 "test")
+printfn "%d" (getFirstOnly (1, "ignored"))
+printfn "%s" (handleEmpty None)