Please could someone explain this rewrite?

Question

Please would someone explain in simple terms what these rules are doing:

RewriteEngine on
RewriteRule .* - [E=HTTP_IF_MODIFIED_SINCE:%{HTTP:If-Modified-Since}]
RewriteRule .* - [E=HTTP_IF_NONE_MATCH:%{HTTP:If-None-Match}]

Answer 1

It's matching any input (.*), and redirecting to the same location, setting the Environmental variables (HTTP_IF_MODIFIED_SINCE and HTTP_IF_NONE_MATCH) equal to the value in the http headers (If-Modified-Since and If-None-Match respectively).

Basically it's just pulling some HTTP Header information and putting it in Environmental variables, presumably for future logic to take some action dependent on the variables.