While creating a custom pop-up (via invoke_props_dialog) with two integer values (in this case representing a start frame and stop frame) I find that the "execute()" method (upon clicking the "ok" button) is when values within my class (derived from Operator) actually get a chance to be used. Intermediate changes to those integers (prior to clicking "ok") cannot be accessed.
I am wondering, if I wanted changes to my start frame integer and stop frame integer to always enforce that start frame is less than or equal to stop frame is there a way to do this prior to clicking "ok"? I am wondering by what method I can take an edit to start frame or stop frame which breaks this condition and force the other to a valid state.
Example, someone increasing start frame integer, as it exceeds stop frame, would force stop frame to increase so as to never break requirements...and to be visible prior to clicking the "ok" button. Is there an ability for invoke_props_dialog to name a callback to run upon any change?