Sorted the string.fsi entries and added examples to each one (#12130)

* Sorted the string.fsi entries and added examples to each one

* Applying suggestions to the String examples

* Following the suggestion that is more clear.

* Sorted the string.fsi entries and added examples to each one

* Applying suggestions to the String examples

* Following the suggestion that is more clear.

src/fsharp/FSharp.Core/string.fsi

@@ -18,6 +18,30 @@ namespace Microsoft.FSharp.Core
     [<RequireQualifiedAccess>]
     module String = 
 
+        /// <summary>Builds a new string whose characters are the results of applying the function <c>mapping</c>
+        /// to each of the characters of the input string and concatenating the resulting
+        /// strings.</summary>
+        ///
+        /// <param name="mapping">The function to produce a string from each character of the input string.</param>
+        /// <param name="str">The input string.</param>
+        ///
+        /// <returns>The concatenated string.</returns>
+        /// 
+        /// <example id="collect-example-1"> The following samples shows how to interspace spaces in a text
+        /// <code lang="fsharp">
+        /// let input = "Stefan says: Hi!"
+        /// input |> String.collect (sprintf "%c ") // evaluates "S t e f a n   s a y s :   H i ! "
+        /// </code>
+        /// </example>
+        /// 
+        /// <example id="collect-example-2"> How to show the ASCII representation of a very secret text
+        /// <code lang="fsharp">
+        /// "Secret" |> String.collect (fun chr -> int chr |> sprintf "%d ")  // evaluates "83 101 99 114 101 116 "
+        /// </code>
+        /// </example>
+        [<CompiledName("Collect")>]
+        val collect: mapping:(char -> string) -> str:string -> string
+
         /// <summary>Returns a new string made by concatenating the given strings
         /// with separator <c>sep</c>, that is <c>a1 + sep + ... + sep + aN</c>.</summary>
         /// <param name="sep">The separator string to be inserted between the strings
@@ -27,54 +51,41 @@ namespace Microsoft.FSharp.Core
         /// <returns>A new string consisting of the concatenated strings separated by
         /// the separation string.</returns>
         /// <exception cref="T:System.ArgumentNullException">Thrown when <c>strings</c> is null.</exception>
+        /// 
+        /// <example id="concat-example-1">
+        /// <code lang="fsharp">
+        /// let input1 = ["Stefan"; "says:"; "Hello"; "there!"]
+        /// input1 |> String.concat " "  // evaluates "Stefan says: Hello there!"
+        /// 
+        /// let input2 = [0..9] |> List.map string 
+        /// input2 |> String.concat ""    // evaluates "0123456789"
+        /// input2 |> String.concat ", "  // evaluates "0, 1, 2, 3, 4, 5, 6, 7, 8, 9"
+        /// 
+        /// let input3 = ["No comma"]
+        /// input3 |> String.concat ","   // evaluates "No comma"
+        /// </code>
+        /// </example>
         [<CompiledName("Concat")>]
         val concat: sep:string -> strings: seq<string> -> string
 
-        /// <summary>Applies the function <c>action</c> to each character in the string.</summary>
-        ///
-        /// <param name="action">The function to be applied to each character of the string.</param>
-        /// <param name="str">The input string.</param>
-        [<CompiledName("Iterate")>]
-        val iter: action:(char -> unit) -> str:string -> unit
-
-        /// <summary>Applies the function <c>action</c> to the index of each character in the string and the
-        /// character itself.</summary>
-        ///
-        /// <param name="action">The function to apply to each character and index of the string.</param>
-        /// <param name="str">The input string.</param>
-        [<CompiledName("IterateIndexed")>]
-        val iteri: action:(int -> char -> unit) -> str:string -> unit
-
-        /// <summary>Builds a new string whose characters are the results of applying the function <c>mapping</c>
-        /// to each of the characters of the input string.</summary>
-        ///
-        /// <param name="mapping">The function to apply to the characters of the string.</param>
-        /// <param name="str">The input string.</param>
-        ///
-        /// <returns>The resulting string.</returns>
-        [<CompiledName("Map")>]
-        val map: mapping:(char -> char) -> str:string -> string
-
-        /// <summary>Builds a new string whose characters are the results of applying the function <c>mapping</c>
-        /// to each character and index of the input string.</summary>
-        ///
-        /// <param name="mapping">The function to apply to each character and index of the string.</param>
-        /// <param name="str">The input string.</param>
-        ///
-        /// <returns>The resulting string.</returns>
-        [<CompiledName("MapIndexed")>]
-        val mapi: mapping:(int -> char -> char) -> str:string -> string
-
-        /// <summary>Builds a new string whose characters are the results of applying the function <c>mapping</c>
-        /// to each of the characters of the input string and concatenating the resulting
-        /// strings.</summary>
+        /// <summary>Tests if any character of the string satisfies the given predicate.</summary>
         ///
-        /// <param name="mapping">The function to produce a string from each character of the input string.</param>
+        /// <param name="predicate">The function to test each character of the string.</param>
         /// <param name="str">The input string.</param>
         ///
-        /// <returns>The concatenated string.</returns>
-        [<CompiledName("Collect")>]
-        val collect: mapping:(char -> string) -> str:string -> string
+        /// <returns>True if any character returns true for the predicate and false otherwise.</returns>
+        /// 
+        /// <example id="exists-example-1"> Looking for uppercase characters
+        /// <code lang="fsharp">
+        /// open System
+        /// 
+        /// "Yoda" |> String.exists Char.IsUpper  // evaluates true
+        /// 
+        /// "nope" |> String.exists Char.IsUpper  // evaluates false
+        /// </code>
+        /// </example>
+        [<CompiledName("Exists")>]
+        val exists: predicate:(char -> bool) -> str:string -> bool
 
         /// <summary>Builds a new string containing only the characters of the input string
         /// for which the given predicate returns "true".</summary>
@@ -85,9 +96,44 @@ namespace Microsoft.FSharp.Core
         /// <param name="str">The input string.</param>
         ///
         /// <returns>The resulting string.</returns>
+        /// 
+        /// <example id="filter-example-1"> Filtering out just alphanumeric characters
+        /// <code lang="fsharp">
+        /// open System
+        /// 
+        /// let input = "0 1 2 3 4 5 6 7 8 9 a A m M"
+        /// input |> String.filter Uri.IsHexDigit  // evaluates "123456789aA"
+        /// </code>
+        /// </example>
+        /// <example id="filter-example-2"> Filtering out just digits
+        /// <code lang="fsharp">
+        /// open System
+        /// 
+        /// "hello" |> String.filter Char.IsDigit  // evaluates ""
+        /// </code>
+        /// </example>
         [<CompiledName("Filter")>]
         val filter: predicate:(char -> bool) -> str:string -> string
 
+        /// <summary>Tests if all characters in the string satisfy the given predicate.</summary>
+        ///
+        /// <param name="predicate">The function to test each character of the string.</param>
+        /// <param name="str">The input string.</param>
+        ///
+        /// <returns>True if all characters return true for the predicate and false otherwise.</returns>
+        ///         
+        /// <example id="forall-example-1"> Looking for lowercase characters
+        /// <code lang="fsharp">
+        /// open System
+        /// 
+        /// "all are lower" |> String.forall Char.IsLower  // evaluates false
+        /// 
+        /// "allarelower" |> String.forall Char.IsLower    // evaluates true
+        /// </code>
+        /// </example>
+        [<CompiledName("ForAll")>]
+        val forall: predicate:(char -> bool) -> str:string -> bool
+
         /// <summary>Builds a new string whose characters are the results of applying the function <c>mapping</c>
         /// to each index from <c>0</c> to <c>count-1</c> and concatenating the resulting
         /// strings.</summary>
@@ -98,26 +144,115 @@ namespace Microsoft.FSharp.Core
         ///
         /// <returns>The constructed string.</returns>
         /// <exception cref="T:System.ArgumentException">Thrown when <c>count</c> is negative.</exception>
+        /// 
+        /// <example id="init-example-1"> Enumerate digits ASCII codes
+        /// <code lang="fsharp">
+        /// String.init 10 (fun i -> int '0' + i |> sprintf "%d ")  // evaluates "48 49 50 51 52 53 54 55 56 57 "
+        /// </code>
+        /// </example>
         [<CompiledName("Initialize")>]
         val init: count:int -> initializer:(int -> string) -> string
 
-        /// <summary>Tests if all characters in the string satisfy the given predicate.</summary>
+        /// <summary>Applies the function <c>action</c> to each character in the string.</summary>
         ///
-        /// <param name="predicate">The function to test each character of the string.</param>
+        /// <param name="action">The function to be applied to each character of the string.</param>
         /// <param name="str">The input string.</param>
+        /// 
+        /// <example id="iter-example-1"> Printing the ASCII code for each characater in the string
+        /// <code lang="fsharp">
+        /// let input = "Hello"
+        /// input |> String.iter (fun c -> printfn "%c %d" c (int c))
+        /// // evaluates unit
+        /// // prints:
+        /// H 72
+        /// e 101
+        /// l 108
+        /// l 108
+        /// o 111
+        /// </code>
+        /// </example>
+        [<CompiledName("Iterate")>]
+        val iter: action:(char -> unit) -> str:string -> unit
+
+        /// <summary>Applies the function <c>action</c> to the index of each character in the string and the
+        /// character itself.</summary>
         ///
-        /// <returns>True if all characters return true for the predicate and false otherwise.</returns>
-        [<CompiledName("ForAll")>]
-        val forall: predicate:(char -> bool) -> str:string -> bool
+        /// <param name="action">The function to apply to each character and index of the string.</param>
+        /// <param name="str">The input string.</param>
+        /// 
+        /// <example id="iteri-example-1"> Numbering the characters and printing the associated ASCII code 
+        /// for each characater in the input string
+        /// <code lang="fsharp">
+        /// let input = "Hello"
+        /// input |> String.iteri (fun i c -> printfn "%d. %c %d" (i + 1) c (int c))
+        /// // evaluates unit
+        /// // prints:
+        /// 1. H 72
+        /// 2. e 101
+        /// 3. l 108
+        /// 4. l 108
+        /// 5. o 111
+        /// </code>
+        /// </example>
+        [<CompiledName("IterateIndexed")>]
+        val iteri: action:(int -> char -> unit) -> str:string -> unit
 
-        /// <summary>Tests if any character of the string satisfies the given predicate.</summary>
+        /// <summary>Returns the length of the string.</summary>
         ///
-        /// <param name="predicate">The function to test each character of the string.</param>
         /// <param name="str">The input string.</param>
         ///
-        /// <returns>True if any character returns true for the predicate and false otherwise.</returns>
-        [<CompiledName("Exists")>]
-        val exists: predicate:(char -> bool) -> str:string -> bool
+        /// <returns>The number of characters in the string.</returns>
+        /// 
+        /// <example id="length-example-1"> Getting the length of different strings
+        /// <code lang="fsharp">
+        /// String.length null   // evaluates 0
+        /// String.length ""     // evaluates 0
+        /// String.length "123"  // evaluates 3
+        /// </code>
+        /// </example>
+        [<CompiledName("Length")>]
+        val length: str:string -> int
+
+        /// <summary>Builds a new string whose characters are the results of applying the function <c>mapping</c>
+        /// to each of the characters of the input string.</summary>
+        ///
+        /// <param name="mapping">The function to apply to the characters of the string.</param>
+        /// <param name="str">The input string.</param>
+        ///
+        /// <returns>The resulting string.</returns>
+        /// 
+        /// <example id="map-example-1"> Changing case to upper for all characters in the input string
+        /// <code lang="fsharp">
+        /// open System
+        /// let input = "Hello there!"
+        /// input |> String.map Char.ToUpper  // evaluates "HELLO THERE!"
+        /// </code>
+        /// </example>
+        [<CompiledName("Map")>]
+        val map: mapping:(char -> char) -> str:string -> string
+
+        /// <summary>Builds a new string whose characters are the results of applying the function <c>mapping</c>
+        /// to each character and index of the input string.</summary>
+        ///
+        /// <param name="mapping">The function to apply to each character and index of the string.</param>
+        /// <param name="str">The input string.</param>
+        ///
+        /// <returns>The resulting string.</returns>
+        /// 
+        /// <example id="mapi-example-1"> Alternating case for all characters in the input string
+        /// <code lang="fsharp">
+        /// open System
+        /// 
+        /// let alternateCase indx chr =
+        ///     if 0 = indx % 2 
+        ///         then Char.ToUpper chr 
+        ///         else Char.ToLower chr
+        /// let input = "Hello there!"
+        /// input |> String.mapi alternateCase  // evaluates "HeLlO ThErE!"
+        /// </code>
+        /// </example>
+        [<CompiledName("MapIndexed")>]
+        val mapi: mapping:(int -> char -> char) -> str:string -> string
 
         /// <summary>Returns a string by concatenating <c>count</c> instances of <c>str</c>.</summary>
         ///
@@ -126,14 +261,13 @@ namespace Microsoft.FSharp.Core
         ///
         /// <returns>The concatenated string.</returns>
         /// <exception cref="T:System.ArgumentException">Thrown when <c>count</c> is negative.</exception>
+        /// 
+        /// <example id="replicate-example-1">
+        /// <code lang="fsharp">
+        /// "Do it!" |> String.replicate 3   // evaluates "Do it!Do it!Do it!"
+        /// </code>
+        /// </example>
         [<CompiledName("Replicate")>]
         val replicate: count:int -> str: string -> string
-
-        /// <summary>Returns the length of the string.</summary>
-        ///
-        /// <param name="str">The input string.</param>
-        ///
-        /// <returns>The number of characters in the string.</returns>
-        [<CompiledName("Length")>]
-        val length: str:string -> int
+