jQuery选择器源码解读（三）：tokenize方法

function tokenize(selector, parseOnly) {
	var matched, match, tokens, type, soFar, groups, preFilters, 
	// 获取缓存中的结果
	cached = tokenCache[selector + " "];

	
	if (cached) {
		// 若是对初始选择器解析（parseOnly!=true），则返回缓存结果，
		// 若不是，则返回0
		return parseonly ? 0 : cached.slice(0);
	}

	
	soFar = selector;
	groups = [];
	// 此处赋值，仅仅用于减少后续代码字数，缩短执行路径
	preFilters = Expr.preFilter;

	while (soFar) {

		// Comma and first run
		
		if (!matched || (match = rcomma.exec(soFar))) {
			if (match) {
				// Don't consume trailing commas as valid
				
				soFar = soFar.slice(match[0].length) || soFar;
			}
			
			
			groups.push(tokens = []);
		}

		matched = false;

		// Combinators
		
		if ((match = rcombinators.exec(soFar))) {
			
			matched = match.shift();
			// 将匹配结果压入tokens数组中
			tokens.push({
				value : matched,
				// Cast descendant combinators to space
				
				type : match[0].replace(rtrim, " ")
			});
			
			// 将关系符之后的字符串赋予soFar，继续解析
			soFar = soFar.slice(matched.length);
		}

		// Filters
		
		for (type in Expr.filter) {
			
			if ((match = matchExpr[type].exec(soFar))
					&& (!preFilters[type] || (match = preFilters[type]
							(match)))) {
				// 将match[0]移除match数组，同时将它赋予matched
				matched = match.shift();
				// 将匹配结果压入tokens数组中
				tokens.push({
					value : matched,
					type : type,
					matches : match
				});
				// 将匹配结果之后的字符串赋予soFar，继续解析
				soFar = soFar.slice(matched.length);
			}
		}

		
		if (!matched) {
			break;
		}
	}

	// Return the length of the invalid excess
	// if we're just parsing
	// Otherwise, throw an error or return tokens
	
	return parseonly ? soFar.length : soFar ? Sizzle.error(selector) :
	// Cache the tokens
	tokenCache(selector, groups).slice(0);
}