3.1 Macro names

A name is any sequence of letters, digits, and the character ‘_’ (underscore), where the first character is not a digit. m4 will use the longest such sequence found in the input. If a name has a macro definition, it will be subject to macro expansion (see section How to invoke macros). Names are case-sensitive.

Examples of legal names are: ‘foo’, ‘_tmp’, and ‘name01’.