there is already a null engine... from the same author os the css engine (robsta).
http://www.gnome.org/~robsta/gtk-null-engine/

I didn't know about the null engine, and the idea I proposed above is very similar -- BUT: The null engine is too barebones. For example, it does not use Cairo. It also does not have progress-bar animation, or many other such features that would be useful for an aspiring engine writer. Would it be too much trouble to create a stand-alone version of Candido (without Murrine, Mist, Nodoka, etc) with additional comments about the inner workings of the engine?

It's so useless to start another engine which uses the same features of clearlooks or murrine... why?

I think I'm not making myself clear. I would like to write and engine, and the simplest way to do it is by modifying an existing engine. In fact, I have done just that in the past, using Aurora as the starting point.

Bad idea.

The trouble is that Aurora has a very messy source, and uses several ugly hacks. I would rather like to start from an engine that provided me with the basic facilities that a novice engine writer would need. Namely, this barebone engine has the following properties: (1) draws all widgets using Cairo, (2) draws a custom focus marker using Cairo, (3) uses progress-bar animation, (4) is configurable through custom gtkrc parameters (a few examples should be included in this hypothetical engine's source), (5) uses the most current APIs and implements the most current code practices (such as having "hints" in the gtkrc file).

This engine would be used not only for aspiring engine writers like myself, but would also serve as a reference implementation or guideline to proper (clean, non-hacky, etc) engine-writing for the latest GTK version.

In any case, even if we do end up disagreeing, I thank you ahead of time for taking your time to read all this. And keep up the great work with Murrine.

PS: I think your Drupal filters are in the wrong order... They are messing up the HTML tags -- EDIT: apparently this only affects the previews?

I think it should be better for you to add a style to clearlooks or murrine... your murrine_draw_newstyle.c

Better documentation regarding the possible options you can use inside of the gtkrc theme file. I know there are comments in there, but they're just sketchy in many places, and it's not terribly exhaustive. I don't just mean how the gtkrc file is structured, but most regarding the specific keywords and features that Murrine offers. That would help me better be able to understand how it works, and/or write better themes for it. Or modify them, as the case may be. I'm not a programmer, so going to look at the code is not going to help me much.