Doc: string examples

doc/Expr.adoc

@@ -194,6 +194,28 @@ Some arithmetic operators can also be used with strings.
 | [blue]`*` | _repeat_ | Make _n_ copy of a string  | [blue]`"one" * 2` _["oneone"]_
 |===
 
+The items of strings can be accessed using the dot `.` operator.
+
+.Item access syntax
+[source,bnf]
+----
+<item> ::= <string-expr>"."<index-expr>
+----
+
+.String examples
+[source,go]
+----
+`>>>` [blue]`s="abc"`  [gray]`// assign the string to variable s`
+[geen]`abc`
+`>>>` [blue]`s.1`      [gray]`// char at position 1 (starting from 0)
+[blue]`b`
+`>>>` [blue]`s.(-1)`   [gray]`// char at position -1, the rightmost one
+[blue]`c`
+`>>>` [blue]`#s`       [gray]`// number of chars
+[blue]3`
+`>>>` [blue]`#"abc"`   [gray]`// number of chars
+[blue]3`
+----
 
 === Boolean
 Boolean data type has two values only: _true_ and _false_. Relational and Boolean expressions produce Boolean values.
@@ -293,6 +315,9 @@ The items of array can be accessed using the dot `.` operator.
 `>>>` [blue]`list.(-1)`
 [green]`three`
 `>>>` [blue]`list.(10)`
+[red]`Eval Error: [1:9] index 10 out of bounds`
+`>>>` [blue]`#list`
+[green]`3`
 ----