Really cool and very fast answer indeed!!!! THANK YOU!!!!
I was about to write I forgot to mention that the $edit-text widget have a focusPopup property, which I have not found out how to use. I saw it apparently required the widget having css class tc-popup-handle. I put my help in focusPopup, but not directly: I use a tiddler name "grid" where I specify the help text (as focusPopup needs to be a tiddler title or perhaps more broadly a tw reference (?)). In my case, the reference was "grid##a3" for instance and in grid (a simple dictionary) I had "a3: A3" (just to show what cell you are editing). But when I clicked on the cell, it has the hidden effect to switch "a3: A3" to something like "a3: (42,142,225,24)".
While I'm at it, I cannot see any reference for style like tc-popup-handle in the standard tw docs. Is there a place to look at for them (apart source code and css classes maybe)?
Ads for tool-tips, accessibility rules insists on having some helps for all kinds of inputs. Surely input widgets would be better having a title option (it's simple and quick, event though it may not be sufficient and then popup mechanism already existing would surely bring the solution).
Regards.