Unicode.Transform.Rule.Definition (Unicode Transform v0.1.0) View Source
10.3.7 Variable Definition Rules
Each variable definition is of the following form:
$variableName = contents ;
The variable name can contain letters and digits, but must start with a letter. More precisely, the variable names use Unicode identifiers as defined by [UAX31]. The identifier properties allow for the use of foreign letters and numbers.
The contents of a variable definition is any sequence of Unicode sets and characters or characters. For example:
$mac = M [aA] [cC] ;
Variables are only replaced within other variable definition rules and within conversion rules. They have no effect on transliteration rules.