Font Layout Table
 
 FLT ::= CATEGORY-TABLE GENERATOR
         [ CATEGORY-TABLE? GENERATOR ]*
 
 CATEGORY-TABLE ::= MAPPER*
 MAPPER ::=
     '(' CHARACTER CATEGORY-LETTER ')'
      | '((' FROM TO ')' CATEGORY-LETTER ')'
 CATEGORY-LETTER ::=
     'A' | ... | 'Z' | 'a' | ... | 'z'
 
 GENERATOR ::= RULE
 RULE ::= '(' MATCHER COMMAND * ')'
 MATCHER ::= REGEXP | SEGMENT-IDX | CODE-RANGE
 COMMAND ::= '<' | '|' | '=' | '*' | ... | RULE