PageSpeed Service was turned off on August 3rd, 2015. Please see Turndown Information for PageSpeed Service.
Objective
Optimize browser rendering by allowing all of the CSS to be specified
in the head
section.
PageSpeed rule
This rewriter implements the PageSpeed rule for optimizing browser rendering.
Description
This rewriter reduces the number of times a browser must re-flow the
document by ensuring that all CSS styles (inline and outlined) are
parsed in the document head
section, before any
body
elements are introduced. All <style>
and <link>
tags, within the head
and
body
sections, are moved to the head
section, in such a way that their relative ordering is preserved.
Operation
This rewriter parses the HTML document, finds all <style>
and <link>
tags and moves these tags to the end of the
head
section.
Example
The example below shows the HTML before rewriting:
<html> <head> </head> <body> <style type="text/css"> .big { font-size: 8em; } </style> <div class="big"> Hello, world! </div> </body> </html>
and after rewriting:
<html> <head> <style type="text/css"> .big { font-size: 8em; } </style> </head> <body> <div class="big"> Hello, world! </div> </body> </html>
Limitations
PSS streams HTML to users, and thus will only see some HTML content
after other content has already been sent to users. If PSS has already
sent the <head>
section to the user, subsequently
discovered CSS elements will not be moved to <head>
.