When I make Column Mode selection (with ALT-key), POS1/END should extend the selection to top or bottom of document. Also PageUp/PageDown makes a little wrong selection in this scenario.
This is a Scintilla desingn issue, so N++ can hardly help.
Scintilla binds keys to messages, and the messages to extend a stream or rectangular selection are different.
You'd need a plugin to detect what's your selection mode and do the right thing. One question though. how will the plugin know that you switched from stream to rectangular or back?
I've found a trick, which allow rectangular selection from cursor position
to the beginning or to the end of a file !
( Of course, cursor can be on the first or on the last line of the file )
1)Click on the column and line you want to start the rectangular selection.
2) Then, scroll to the line, where the rectangular selection must end,
by moving the lift up or down, on the right edge of the window
( DON'T use shortcuts, like CTRL + End and so on : cursor must not move ! ).
3) On the line, where the rectangular selection must end, do a ALT + SHIFT + Click
on any column, to create the rectangular selection
4) Adjust, with the two shortcuts ALT + SHIFT + Left Arrow and/or ALT + SHIFT + Right Arrow, to get the right width you want to, even nul !
5) Finally, delete this selection or write an eventual text, you would like to insert, instead.
Indeed, concerning the beginning / end of a file, there are 4 Scintilla commands :
SCI_DOCUMENTSTART, SCI_DOCUMENTSTARTEXTEND, SCI_DOCUMENTEND and SCI_DOCUMENTENDEXTEND
But, the Scintilla commands SCI_DOCUMENTRSTARTRECTEXTEND and SCI_DOUCMENTENDRECTEXTEND don't exist !
You can also use Ctrl+Home or Ctrl+End to move the cursor to the beginning or end of the document.
If you set your cursor position to the other edge, then press and hold the Shift button and then press Ctrl+Home or Ctrl+End, you will get a normal selection.
All you then have to do is hold the Shift button, press and hold Alt, press and hold CursorLeft or CursorRight and then the opposite to get a rectangular selection (or adjust it right away to the desired width).
I never tried your method before, but I agree it's more simple than mine !
I don't even understand, why I didn't find out this trick, as I'm rather "shortcut's fan" with use of minimum mouse gestures !