code: function(walk) {
      if (!walk.at("\\"))
        return false;
      // Assuming backslash
      walk.skip();
      if (walk.matchSome(backslashChars)) {
        this.out.push(walk.current());
        walk.skip();
      } else {
        this.out.push("\\");
      }
      return true;
    }
docs: /* Reserved char are backslash-escaped.