Let's say we have two class to define form elements (for example, the module mytabs):


Is it possible to incorporate elements of the form in one class to another?
For example...

could show TabForm with elements from PageForm (between 'tabtitle' and 'tabfromdate').
You know... If you want to change the items in PageForm you need to modify this one class rather than two.

It does not concern me about this particular module, but the overall concept. How to solve for classes?

XoopsForm is a rather simple class for making HTML forms. It needs that the formelements (elements that make the form, like inputs and texts) are added in the order of displaying to the form.
I do not fully understand your question, (because the references to your example code is not always clear or consequent) but I assume you would like to have some regular used group of formelements as form blocks, which are then to be used to build the form.
There are several ways to work this out:
- You extend the form class to eg BlockThemeForm with a function that can add its elements to another form eg AddToForm .
From that BlockThemeForm you can derive a new form eg MyFormTabs, that adds automatic some elements in its construct (similar to your examples).
Then you do:

Other way is to extend FormElements to have more items at once. There is already an element that does this in a grouped manner eg XoopsFormElementTray An extension or similar class, could also allow to add some grouped elements to a form.
Have also a look at the cross reference documentation at XooFoo.

This code is inside MytabsTab class and calls that form by passing itself into it ($this).

The Form class is dependent on this Object class. Actually, there was no need to have a form class. I could have build the form inside the object class.

Anyway, after you create elements you can use getElements()

$myelements[] = $form1->getElements();
$myelements[] = $form2->getElements();

each element can be rendered with no need to be inside a form.
you can do
echo "foreach ($myelements as $ele) {echo $ele->render();}
echo "";

Or you can build a themeform and use the label element containing the rendered elements.