Paste: Single-line pastes should conform to current block

[mcsf]

Issue Overview

A revisit of #5354. Per the last comment, this is the behavior we'd like to achieve when copying (a) list item(s) from a rich-text source:

• If you are on an empty paragraph, respect the source [and create a new list block, for instance].
• Otherwise, if you copied more than one line, respect the source [and create a new list block, for instance].
• Otherwise, if you copy a single line, paste as plain text [and merely add to the current paragraph].

The last point is where behavior differs: currently, pasting will always create a new block (for a list, etc.) unless the clipboard only contains pure text.

[ellatrix]

Sure. So how do we determine that something is a single line?

<ul><li>If you are on an empty paragraph, respect the source [and create a new list block, for instance].</li></ul>

<pre><code>A huge chunk of code</code></pre>

We'll have to specifically target some kind of blocks?

[mcsf]

@iseulde: we would probably start small and focus on lists first, as they are the kind of content that sparked this discussion.

[mtias]

We could try a char-length cutout as well.

[mcsf]

@mtias, can you elaborate?

[mtias]

If the source has less than x length, we treat it as plain text.