Edit operations like copy, paste and select all
Somebody pointed out that we cannot use Ctrl-A to select all in Varamozhi windows. That is true. However, one could right-click to get a popup menu which lists various edit operations including copy, paste and select all. Also, ctrl-c, ctrl-v and ctrl-x do work as expected.
By accident, I discovered that Ctl-/ (Control foraward-slash) selects the entire content in the window.
This Tk Manual describes various other control commands possible in the editing window.