one of the features of ERE is that it's actually a regular language
and does not admit expressions which cannot be matched in linear time.
introduction of \n backref support into regcomp's ERE parsing was
unintentional.
+ if (!ere && isdigit(*s)) {
/* back reference */
int val = *s - '0';
node = tre_ast_new_literal(ctx->mem, BACKREF, val, ctx->position);
/* back reference */
int val = *s - '0';
node = tre_ast_new_literal(ctx->mem, BACKREF, val, ctx->position);