Bring jQuery('#id') and jQuery('body') logic back into core (while leaving it in Sizzle at the same time). Was causing too much of a performance hit to leave it all to Sizzle.

src/core.js

@@ -15,8 +15,9 @@ var jQuery = function( selector, context ) {
 	// A central reference to the root jQuery(document)
 	rootjQuery,
 
-	// A simple way to check for HTML strings
-	quickExpr = /^[^<]*(<[\w\W]+>)[^>]*$/,
+	// A simple way to check for HTML strings or ID strings
+	// (both of which we optimize for)
+	quickExpr = /^(?:[^<]*(<[\w\W]+>)[^>]*$|#([\w\-]+)$)/,
 
 	// Check if a string has a non-whitespace character in it
 	rnotwhite = /\S/,
@@ -92,10 +93,25 @@ jQuery.fn = jQuery.prototype = {
 			return this;
 		}
 
+		// The body element only exists once, optimize finding it
+		if ( selector === "body" && !context && document.body ) {
+			this.context = document;
+			this[0] = document.body;
+			this.selector = "body";
+			this.length = 1;
+			return this;
+		}
+
 		// Handle HTML strings
 		if ( typeof selector === "string" ) {
-			// Are we dealing with HTML string
-			if ( (match = quickExpr.exec( selector )) ) {
+			// Are we dealing with HTML string or an ID?
+			match = quickExpr.exec( selector );
+
+			// Verify a match, and that no context was specified for #id
+			if ( match && (match[1] || !context) ) {
+
+				// HANDLE: $(html) -> $(array)
+				if ( match[1] ) {
 					context = context instanceof jQuery ? context[0] : context;
 					doc = (context ? context.ownerDocument || context : document);
 
@@ -119,6 +135,29 @@ jQuery.fn = jQuery.prototype = {
 
 					return jQuery.merge( this, selector );
 					
+				// HANDLE: $("#id")
+				} else {
+					elem = document.getElementById( match[2] );
+
+					// Check parentNode to catch when Blackberry 4.6 returns
+					// nodes that are no longer in the document #6963
+					if ( elem && elem.parentNode ) {
+						// Handle the case where IE and Opera return items
+						// by name instead of ID
+						if ( elem.id !== match[2] ) {
+							return rootjQuery.find( selector );
+						}
+
+						// Otherwise, we inject the element directly into the jQuery object
+						this.length = 1;
+						this[0] = elem;
+					}
+
+					this.context = document;
+					this.selector = selector;
+					return this;
+				}
+
 			// HANDLE: $(expr, $(...))
 			} else if ( !context || context.jquery ) {
 				return (context || rootjQuery).find( selector );