public function by( $key, $value ) {
		if ( $this->void_query ) {
			// No point in doing more computations if the query is void.
			return $this;
		}

		$call_args = func_get_args();

		$this->current_filters[ $key ] = $value;

		try {
			$query_modifier = $this->modify_query( $key, $call_args );

			/**
			 * Here we allow the repository to call one of its own methods and return `null`.
			 * A repository might have a `where` or `by` that is just building
			 * a more complex query using a base `where` or `by`.
			 */
			if ( null === $query_modifier ) {
				return $this;
			}

			/**
			 * Primitives are just merged in.
			 * Since we are using `array_merge_recursive` we expect them to be arrays.
			 */
			if ( ! ( is_object( $query_modifier ) || is_callable( $query_modifier ) ) ) {

				if ( ! is_array( $query_modifier ) ) {
					throw new InvalidArgumentException( 'Query modifier should be an array!' );
				}

				$replace_modifiers = in_array( $key, $this->replacing_modifiers(), true );
				if ( $replace_modifiers ) {
					/**
					 * We do a merge to make sure new values will override and replace the old
					 * ones.
					 */
					$this->query_args = array_merge( $this->query_args, $query_modifier );
				} else {
					/**
					 * We do a recursive merge to allow "stacking" of same kind of queries;
					 * e.g. two or more `tax_query`.
					 */
					$this->query_args = array_merge_recursive( $this->query_args, $query_modifier );
				}
			} else {
				/**
				 * If we get back something that is not an array then we add it to
				 * the stack of query modifying callbacks we'll call on the query
				 * after building it.
				 */
				$this->query_modifiers[] = $query_modifier;
			}
		} catch ( Tribe__Repository__Void_Query_Exception $e ) {
			/**
			 * We allow for the `apply` method to orderly fail to micro-optimize.
			 * If applying one parameter would yield no results then let's immediately bail.
			 * Schema should throw t
			 * his Exception if a light-weight on the filters would already
			 * deem a query as yielding nothing.
			 */
			$this->void_query = true;

			return $this;
		}

		/**
		 * Catching other type of exceptions is something the client code should handle!
		 */

		return $this;
	}