function Ruler() {
  // List of added rules. Each element is:
  //
  // { name: XXX,
  //   enabled: Boolean,
  //   fn: Function(),
  //   alt: [ name2, name3 ] }
  //
  this.__rules__ = [];

  // Cached rule chains.
  //
  // First level - chain name, '' for default.
  // Second level - digital anchor for fast filtering by charcodes.
  //
  this.__cache__ = null;
}
Ruler is a helper class for building responsibility chains from
parse rules. It allows:

  - easy stack rules chains
  - getting main chain and named chains content (as arrays of functions)

Helper methods, should not be used directly.
@api private