When working with CSS in the CSS Registry, each stylesheet has some parameters that can be tweaked.

id

The Zope id of the stylesheet to be used.

expression

A CMF expression to be evaluated to check if the stylesheet should be included in output or not.

media

The media for which the stylesheet should apply, normally empty or 'all'. other possible values are 'screen', 'print' etc. Read more about the media settings of CSS at w3.org

rel

Link relation. defaults to 'stylesheet', and should almost always stay that way. For designating alternative stylesheets. This is used for the toggle between large, medium and small fonts in default Plone. Don't change this one unless you know what you are doing.

title

the title of an alternate stylesheet.

rendering

How the stylesheet is linked from the html page. This is an advanced setting. Leave it set to the default 'import' unless you know the effects of different ways of rendering and linking stylesheets

import

the default. normal css import

link

works better for old browsers and is needed for alternate stylesheets

inline

render the stylesheet inline instead of linking it externally. Shouldn't be used at all! It isn't possible to create sites which validate if you do.
For more information see: http://developer.mozilla.org/en/docs/Properly_Using_CSS_and_JavaScript_in_XHTML_Documents

compression

Whether and how much the resource should be compressed

none

the original content will not be changed

safe

the content will be compressed in a way which should be safe for any workarounds for browser bugs. Conditional code for Internet Explorer is preserved since ResourceRegistries 1.2.3 and 1.3.1.

full

the content will be compressed with some additional rules.For css all comments and most newlines are removed, this may break special browser hacks, so use with care. For javascript this encodes variables with special prefixes according to the rules described here (Special Characters):
http://dean.edwards.name/packer/usage/ The source code needs to be written according to those rules, otherwise it's more than likely that it will break.

safe-encode

- only available for javascript
- 'full-encode' - only available for javascript. Additionally encodes keywords. This heavily compresses the javascript, but it needs to be decoded on the fly in the browser on each load. Depending on the size of the scripts this could lead to timeouts in Firefox. Use with special care!