[Lazarus] Developing a WidgetSet

[Lubos Pintes]

Hello,
If I want to add a functionality like accessibility to WidgetSet, which 
package could I use, lcl.lpk, or lclbase.lpk?
Also, how can I rebuilt the package when I modify/add some unit? Do I 
need to always rebuild the IDe, or there is a quicker way?
I am thinking about syntax check / quick compilation to incrementally 
check and fix semantic / syntax errors.

Thanks