DAJAXValidationItem
With the experiences from my last plug in I wrote a second more powerful validation plug in. It can validate against a user defined PL/SQL function and gives the developers the flexibility to write their own validation directly in the item.
DAJAXValidationItem Settings
DRegExItem
With ApEx 4 we are able to shift a few kinds of validation directly to the items. Some of them are released with ApEx 4 like the “Number Textfield” or the “Value Required” selection box within the item configuration. But there are several other syntax related validations like telephone number, zip code or email addresses. Therefore I wrote a plug in, that validate the value against a Regular Expression and we can move most of the syntax validations to our items and making them responsible for that.
After a new installation of Oracle XE, I found that I cannot access the Apex website from remote, although the configuration for the firewall seems to be correct and the 8080 port is reachable. After hours with my friend Dr. Google I found the solution (again) and this post is more or less a reminder for me when I set up a new Oracle XE instance with ApEx next time. 
Just wrote my very first plug in for ApEx 4.0:
DTreeTable ApEx Plugin puts hierarchical data in columns, but use an indented outline structure in the first column to illustrate the tree structure.
Combining the two data-viewing approaches into one view gives you the best of both worlds. You can show the hierarchy of items, plus a matrix of additional data or item attributes, in one unified structure.
I needed to know when an Interactive Report was refreshed, since somebody changes the filters or whatever. Within ApEx 4.0 you can declare Dynamic Actions but it was not possible to implement the “After Refresh” event on the Interactive Report region. It is allegeable, because the region does not contain only the data grid, but also other components like the search bar or the pagination. Therefore you cannot connect a Dynamic Action with the Interactive Report region directly, but how can I add an observer to the Interactive Report?