At the moment, object attributes (e.g. in an input field etc.) seem to limited to those available through the regular GUI, while adding them manually in the HTML->Attributes input subform. Anyway, adding things like "onfocus" etc. can be entered, but will not show up in the code ... it would be nice if attributes not directly supported in the GUI part could still be entered there ... (or am I missing something / doing something wrong?)
There have been many threads discussing this issue. The developers have disabled certain "on" attributes for security reasons in the HTML (onInput, onFocus, etc) and it get stripped away without any notice. If you do a search in the forum you'll see many posts about.