function skipIfHasPrecedingDot(match, response) {
    const before = match.input[match.index - 1];
    if (before === ".") {
      response.ignoreMatch();
    }
  }
Skip a match if it has a preceding dot

This is used for `beginKeywords` to prevent matching expressions such as
`bob.keyword.do()`. The mode compiler automatically wires this up as a
special _internal_ 'on:begin' callback for modes with `beginKeywords`
@param {RegExpMatchArray} match
@param {CallbackResponse} response