A syntax table is an array indexed by the characters in your character set. In the ASCII encoding, therefore, a syntax table has 256 elements.
If Regex is compiled with the preprocessor symbol
then Regex expects you to define and initialize the variable
re_syntax_table to be an Emacs syntax table. Emacs’ syntax
tables are more complicated than Regex’s own (see Non-Emacs Syntax Tables). See Syntax in The GNU Emacs User’s Manual,
for a description of Emacs’ syntax tables.