I am building a real world web app with Castle Project right now. So, the debugging is done for IE. And I encountered two different things of interest:
1. Javascript-based form validation as it’s implemented for Castle Project does not work in Opera. Even more, pressing submit button in Opera causes a big stack trace of errors. Correct me, if I’m wrong, that’s because IE’s lack of standarts. I really
dont know what’s the problem is, because I’m not a tough javascript programmer.
2. IE automagically handles OPTION tag insertions into select lists. I have complex form, with a lot of selects, most of them have other selects as parents. E.g. City has District and Street as children. So I want to populate District and Street using ajax call invoked using onchange event hook of City select. I have two invocations for each one of the two. I pass District Select Id to the Ajax.Request object. And what I wanted to do was to simply get a lot of lines like

…
< value=”district_id”>district_name
…

by parsing my NVelocity template. And actually the code did return right list of options. But when it tried to insert them into District Select (with javascript using innerHTML property, I think. read about Prototype js library here) in IE 6 that resulted in messed tags (i use IE Developer Toolbar to see changes):

…
district_name<>< /option>< /option>< //option>
…

In Opera however, that didn’t happen and it worked just as it was expected to. So after 2 hours of trying to understand what’s going on, I found explanation to this. The thing is, MS does not allow option tag insertions without corresponding select tags. So, be concerned about this.