Validation - Maximium limit for characters in VFE

System

Hi,

I want to set the max limit for the characters in visual format editor. how can i do that.
for eg. i tried this for 100 characters.

validation-regex="^.{0,100}$"
and
validation-regex="^.\{0,100\}$"

but the exapmle works fine only for the textarea not for VFE. Should i use Form API. Any suggestions will be grateful.

Thanks