Update string truncation behavior

[j-f1]

This should look visually similar, but selecting and copying a truncated string will now copy the entire string (excluding the “…”), even the portion that is not visible.

I have also changed the ellipsis from the standard ellipsis character (…), which can easily be missed, to a more obvious ••• rendered in black so it is clearly not part of the string.

[j-f1]

Would it be possible to get this merged? It annoys me that it’s really hard to copy out long strings from notebooks.

[mootari]

I believe the ellipsis is not only a visual aid for long strings, but also avoids rendering excessively large strings in the DOM. Under that premise you'd have to pick a different strategy. Some suggestions:

• replace the ellipsis with its masked content on click
• allow truncated strings to be expanded (like we do for arrays and objects), revealing the entire string line-wrapped
• detect copy events, determine whether the ellipsis text node is in the selection range, and replace it with the actual content
• add an explicit copy button (e.g. on hover)