So, any of you who have used X-Windows (ok, ok, The X Windowing System, but that's a mouthful) for long, especially with a lot of use of xterms will know the default annoyance that is copy and pasting between xterms and more modern X apps.
Basically when you highlight text using the mouse in an xterm it gets put into a buffer that the middle mouse button can then paste. That middle mouse button will even work to paste, for example, into the location bar in Firefox. What doesn't work is hitting Ctrl-V or Shift-Insert in that location bar to paste in what you just highlighted.
So, off to Google I go, and I find David Simmons'
xterm hack page. This includes a source-level patch to xterm to make it also place highlighted text into the clipboard buffer, from where it can be Ctrl-V'd or similar. Passing mention is made on that page of it being possible to achieve the same thing with entries in .Xdefaults, as all the source patch is doing is to change the default setting of the translations XResource for XTerm.
Cue my spending a frustrating half hour trying to find documentation on how to specify XResources so as to change part of a resource without specifying it all. After all, I don't want to have ALL the Xterm translations resource in my ~/.Xdefaults, as then if it changes upstream I won't get the change.
Eventually, after ranting to someone else about this, they pointed me to the solution, which it turns out I'd come across/found anyway, just when reading the relevant page(s) I'd been too focussed on trying to find generic documentation for things like exactly what #override does.
Anyway, if you want to achieve what I described, just sling this in your ~/.Xdefaults:
XTerm*VT100.Translations: #override\n\\
Shift Select:select-cursor-start() select-cursor-end(PRIMARY, CLIPBOARD, CUT_BUFFER0) \n\\
Shift Insert:insert-selection(PRIMARY, CLIPBOARD, CUT_BUFFER0) \n\\
~Ctrl ~Meta :insert-selection(SELECT, CLIPBOARD, CUT_BUFFER0)\n\\
:select-end(PRIMARY, CLIPBOARD, CUT_BUFFER0)
You'll need to restart X to have it take full effect.