add StringIndexError documentation (#26747)

NEWS.md

@@ -230,7 +230,7 @@ This section lists changes that do not have deprecation warnings.
  * `countlines` now always counts the last non-empty line even if it does not
  end with EOL, matching the behavior of `eachline` and `readlines` ([#25845]).
 
- * `getindex(s::String, r::UnitRange{Int})` now throws `UnicodeError` if `last(r)`
+ * `getindex(s::String, r::UnitRange{Int})` now throws `StringIndexError` if `last(r)`
  is not a valid index into `s` ([#22572]).
 
  * `ntuple(f, n::Integer)` throws `ArgumentError` if `n` is negative.
@@ -1446,4 +1446,4 @@ Command-line option changes
 [#26436]: https://github.com/JuliaLang/julia/issues/26436
 [#26442]: https://github.com/JuliaLang/julia/issues/26442
 [#26600]: https://github.com/JuliaLang/julia/issues/26600
-[#26670]: https://github.com/JuliaLang/julia/issues/26670
+[#26670]: https://github.com/JuliaLang/julia/issues/26670

base/strings/string.jl

@@ -1,5 +1,10 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
+"""
+ StringIndexError(str, i)
+
+An error occurred when trying to access `str` at index `i` that is not valid.
+"""
 struct StringIndexError <: Exception
  string::AbstractString
  index::Integer

doc/src/base/base.md

@@ -295,6 +295,7 @@ Core.TypeError
 Core.UndefKeywordError
 Core.UndefRefError
 Core.UndefVarError
+Base.StringIndexError
 Base.InitError
 Base.retry
 Base.ExponentialBackOff

doc/src/manual/control-flow.md

@@ -584,7 +584,7 @@ below all interrupt the normal flow of control.
 | [`TypeError`](@ref) |
 | [`UndefRefError`](@ref) |
 | [`UndefVarError`](@ref) |
-| `UnicodeError`  |
+| [`StringIndexError`](@ref) |
 
 For example, the [`sqrt`](@ref) function throws a [`DomainError`](@ref) if applied to a negative
 real value: