code: function filterOnDensity( wordCombinations, wordCount, lowerLimit, upperLimit ) {
  	return wordCombinations.filter( function( combination ) {
  		return ( combination.getDensity( wordCount ) >= lowerLimit && combination.getDensity( wordCount ) < upperLimit
  		);
  	} );
  }
docs: Filters word combinations based on keyword density if the word count is 200 or over.
  
  @param {WordCombination[]} wordCombinations The word combinations to filter.
  @param {number} wordCount The number of words in the total text.
  @param {number} lowerLimit The lower limit of keyword density.
  @param {number} upperLimit The upper limit of keyword density.
  @returns {WordCombination[]} Filtered word combinations.