[DOC] Enhanced RDoc for String (#5742)

Treats:
    #force_encoding
    #b
    #valid_encoding?
    #ascii_only?
    #scrub
    #scrub!
    #unicode_normalized?
Plus a couple of minor tweaks.

1 files changed, 14 insertions, 0 deletions

diff --git a/doc/string/b.rdoc b/doc/string/b.rdoc
new file mode 100644
index 0000000000..f8ad2910b4
--- /dev/null
+++ b/doc/string/b.rdoc
@@ -0,0 +1,14 @@
+Returns a copy of +self+ that has ASCII-8BIT encoding;
+the underlying bytes are not modified:
+
+  s = "\x99"
+  s.encoding   # => #<Encoding:UTF-8>
+  t = s.b      # => "\x99"
+  t.encoding   # => #<Encoding:ASCII-8BIT>
+
+  s = "\u4095" # => "䂕"
+  s.encoding   # => #<Encoding:UTF-8>
+  s.bytes      # => [228, 130, 149]
+  t = s.b      # => "\xE4\x82\x95"
+  t.encoding   # => #<Encoding:ASCII-8BIT>
+  t.bytes      # => [228, 130, 149]