replace mask by switching between Tab Pages

[hudo]

Hello,

I have a canvas MYMAIN (canvas-type Content) which contains the "insert query" part/blocks. Than I have a canvas TABWALL (canvas-type Tab) which contains several
Tab Pages, one for scott.emp one for scott.dept. The canvas TABWALL is a little bit shifted compared to MYMAIN (TABWALL has a viewport x position 150 and a viewport y position 75). Now the question:
if the cursor/focus is on the TabPage with scott.emp, a forms-mask should appear left on MYMAIN where you can enter into two text items two values as limits for scott.emp.sal for querying the scott.emp table.
if the cursor/focus switches to the TabPage with scott.dept, the forms-mask (on MYMAIN ) described above should be replaced by another forms-mask for querying the scott.dept table (for example a text item where you insert a "deptno" and the corresponding record is then displayed on the TabPage with scott.dept.

How can I replace/overwrite a mask by switching between Tab Pages ??
Each Tab Page should so have a corresponding "query mask" on the MYMAIN.

Thanks in advance