Get rid of redundant whitespace & empty structural elements, in that order

jquery.lipo.js

void function semanticContentScope(context, jQuery){
	var $ = context.jQuery || jQuery || false;

	if(!$){
		return false;
	}

	// Strips elements of duplicate, leading and trailing whitespace and removes empty non-functional elements recursively
	function semanticContent(markup){
		// Conversion
		if(markup instanceof HTMLElement){
			markup = markup.outerHTML;
		}
		
		// If nothing was passed, or we were just passed a string full of whitespace, return empty string
		if(!markup && /^\s*$/.test(markup)){
			return '';
		}

		// Wrap contents, add each node to collection, and inverse order:
		// Start at the bottom of the tree, such that recursive iteration removes elements containing nothing but empty elements
		var $wrapper  = $('<div>').append(markup);
		var $contents = $wrapper.add($wrapper.find('*'));
		var $reversed = [].reverse.call($contents);

		// Iterate through each element, starting with end nodes and working up
		$reversed.each(function lipoIterator(index, el){
			var $el    = $(el);
			var markup = el.innerHTML;

			// These rules only apply to known structural and styling elements:
			// We shouldn't be removing or tampering with, ie, <img>s or <hr>s
			if(!/^(b|bold|br|em|font|mark|span|strong|p|div|u)$/i.test(el.tagName)){
				return;
			}

			// If the node contains nothing but whitespace, nerf it
			if(/^br$/i.test(el.tagName) || !markup.replace(/\s|&(nbsp|#160);|<br\/?>/gi,'').length){
				$el.remove();
			}
			else {
				// Replace contents with whitespace-sanitized version
				$el.html(markup
					// Replace encoded non-breaking spaces with breaking spaces
					.replace(/&(nbsp|#160);/gi,' ')
					// Trim leading and trailing whitespace
					.replace(/^\s+|\s+$/g, '')
					// Deduplicate whitespace
					.replace(/(\s){2,}/g, function(multiple,instance){
						return instance;
					})
				);
			}
		});

		return $reversed.eq(-1).html();
	}

	$.fn.semanticContent = function $semanticContentScope(){
		var $yield = $();

		this.each(function(){
			$yield.add($(semanticContent(this));
		});

		return $yield;
	};

	context.semanticContent = semanticContent;
}(this, jQuery);