code: function compIndex(schema, root, baseId) {
    /* jshint validthis: true */
    for (var i=0; i<this._compilations.length; i++) {
      var c = this._compilations[i];
      if (c.schema == schema && c.root == root && c.baseId == baseId) return i;
    }
    return -1;
  }
docs: Index of schema compilation in the currently compiled list
  @this   Ajv
  @param  {Object} schema schema to compile
  @param  {Object} root root object
  @param  {String} baseId base schema ID
  @return {Integer} compilation index