Textpattern has an amazingly flexible system of templates, forms, and plug-ins, but the next version (4.0.7) will improve it’s XML-based tag parser many times over.

The improvements to nested tag parsing will be a nice step up, but the attribute value parsing, esp. the ability to put Textpattern tags within attributes for function-like—well—functionality, will be quite a leap. Currently asy_wondertag provides the ability to parse tags within Textpattern tag attributes, but the other fixes will make this really shine.