async="async" attribute of a <script> tag in html, What does it mean?

Question

async="async" attribute of a tag in html, What does it mean?

Can be see used here for example

Answer 1

It's part of the HTML5 proposal

Answer 2

If the async attribute is set on an external script (one with src=), browsers that support it will download that script in the background without blocking the rest of the content on the page. The script will execute whenever it is finished downloading.

http://dev.w3.org/html5/spec/Overview.html#attr-script-async

As I mentioned in a comment, setting async=true, async=false or async=anything all mean the same thing. They enable the async behavior. The only way to make a script non-async is to completely omit the attribute.

http://dev.w3.org/html5/spec/Overview.html#boolean-attributes