I'd suggest that we use block caret (in addition to the current ctrl+click) also for alt+click so one doesn't have to remember which one is ctrl and which one is alt.
I just tried ``` SSM(sci, SCI_SETRECTANGULARSELECTIONMODIFIER, SCMOD_CTRL | SCMOD_ALT, 0); ``` and sadly, it doesn't work. But since `SCMOD_CTRL=2, SCMOD_ALT=4`, maybe Scintilla could be modified to support both of them in parallel.