(Creating Strings): Argument START to `substring' can not be `nil'.

(Creating Strings): Argument START to `substring' can not be `nil'.
Expand description of `substring-no-properties'.  Correct description
of `split-string', especially with respect to empty matches.  Prevent
very bad line break in definition of `split-string-default-separators'.
(Text Comparison): `string=' and `string<' also accept symbols as
arguments.
(String Conversion): More completely describe argument BASE in
`string-to-number'.
(Formatting Strings): `%s' and `%S" in `format' do require corresponding
object.  Clarify behavior of numeric prefix after `%' in `format'.
(Case Conversion): The argument to `upcase-initials' can be a character.