xhtml - HTML Cache control

Question

What is the difference between below 3 meta tags?

<META HTTP-EQUIV="PRAGMA" CONTENT="NO-CACHE">
<META HTTP-EQUIV="CACHE-CONTROL" CONTENT="NO-CACHE">
<META HTTP-EQUIV="Expires" CONTENT="-1">

Do I need to use all those tags to avoid browser caching?

Answer 1

See the Caching Tutorial for Web Authors and Webmasters which explains about all the different cache control headers (especially the part the explains that those meta tags are largely useless and real HTTP headers are the way forwards).