jQuery选择器源码解读（二）：select方法

function select(selector, context, results, seed) {
	
	var i, tokens, token, type, find, 
	// 调用tokenize函数解析selector
	match = tokenize(selector);

	// 若没有提供初始集合
	if (!seed) {
		// Try to minimize operations if there is only one group
		// 若只有一组选择器，即选择器字符串没有逗号
		if (match.length === 1) {
			// Take a shortcut and set the context if the root selector
			// is an ID
			
			tokens = match[0] = match[0].slice(0);
			
			if (tokens.length > 2 && (token = tokens[0]).type === "ID"
					&& support.getById && context.nodeType === 9
					&& documentIsHTML && Expr.relative[tokens[1].type]) {

				// 将当前上下文指向第一个ID选择器指定的节点对象
				context = (Expr.find["ID"](token.matches[0].replace(
						runescape, funescape), context) || [])[0];
				
				// 若当前上下文内没有指定ID对象，则直接返回results
				if (!context) {
					return results;
				}
				
				// 选择器字符串去掉第一个ID选择器
				selector = selector.slice(tokens.shift().value.length);
			}

			// Fetch a seed set for right-to-left matching
			
			
			
			i = matchExpr["needsContext"].test(selector) ? 0
					: tokens.length;
			while (i--) {
				token = tokens[i];

				// Abort if we hit a combinator
				// 遇到关系符跳出循环
				if (Expr.relative[(type = token.type)]) {
					break;
				}
				if ((find = Expr.find[type])) {
					// Search, expanding context for leading sibling
					// combinators
					
					if ((seed = find(token.matches[0].replace(
							runescape, funescape), rsibling
							.test(tokens[0].type)
							&& context.parentNode || context))) {

						// If seed is empty or no tokens remain, we can
						// return early
						// 剔除刚用过的选择器
						tokens.splice(i, 1);
						selector = seed.length && toSelector(tokens);
						
						if (!selector) {
							push.apply(results, seed);
							return results;
						}

						break;
					}
				}
			}
		}
	}

	// Compile and execute a filtering function
	// Provide `match` to avoid retokenization if we modified the
	// selector above
	
	compile(selector, match)(seed, context, !documentIsHTML, results,
			rsibling.test(selector));
	return results;
}