ONIG_SYN_OP_QMARK_ZERO_ONE  678 regint.h           ONIG_SYN_OP_QMARK_ZERO_ONE | \
ONIG_SYN_OP_QMARK_ZERO_ONE 3643 regparse.c           if (! IS_SYNTAX_OP(syn, ONIG_SYN_OP_QMARK_ZERO_ONE)) break;
ONIG_SYN_OP_QMARK_ZERO_ONE   68 regsyntax.c        ONIG_SYN_OP_PLUS_ONE_INF | ONIG_SYN_OP_QMARK_ZERO_ONE | ONIG_SYN_OP_VBAR_ALT )
ONIG_SYN_OP_QMARK_ZERO_ONE   91 regsyntax.c        ONIG_SYN_OP_QMARK_ZERO_ONE | ONIG_SYN_OP_DECIMAL_BACKREF |