Attaching a proposed patch. If someone is inclined to look at this. A few notes on the patch:
1) Of course, a comitter needs to review and agree on where/how/what the patch implements.
Summary: It adds a lazily instantiated map to AbstractFormTag as well as default implementation of setDynamicAttribute from the DynamicAttribute interface. It does not declare AbstractFormTag as an implementor of DynamicAttribute (just gives a default impl of the method for convenience.) Next, AbstractHtmlElementTag added call writeDynamicAttributes akin to writeOptionalAttributes. Finally, declare AbstractHtmlInputElementTag to implement DynamicAttributes (marker interface for containers to accept/support DynamicAttributes and the assumption is that this is the base class we want to support dynamic attributes on?)
2) I'm not familiar with Ivy or the build process. I know maven so... mvn clean compile executes successfully (after a few pom tweaks on my end like changing javax.activation dependency to geronimo-spec version of it etc..Just my preference to get the build running) but...
3) mvn clean install fails with a couple of test compilation failures unrelated to the patch it seems. Not sure if these are supposed to work or if maven is really used, etc. But without being able to compile the test suite I've tried to emphasize "draft". So hopefully someone finds this a useful start.