Disable ini page next button UltraModernUI

Hi
Can someone please help me. Im a newbie in NSIS, Im using a UltraModernUI and i hava custom ini page. This page contains a DIR REQUEST. USer can also type the directory path. I need to do the following

Case 1..
If user enters invalid text (like abc) disable the Next button or display a message.

Case 2..
If the directory path contains any of the following
CON, PRN, AUX, CLOCK$, NUL COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9 LPT0, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9
disable the Next button or display a message.

Case 3
Enable the Next button on valid path input..

Please help me with this...
Thanks in advance.

Easy solution:
The easy way would to be do the checking the
"MUI_PAGE_CUSTOMFUNCTION_LEAVE"
There you can do your checking and if fails call abort, so the user cannot leave through the "next" button (with a nice infobox what went wrong :-) )
Example:


to achieve exactly what you want: