Cursor behaviour when navigating around blank lines

Description

Blank lines (as opposed to paragraph breaks) can be inserted with shift-enter. However, the cursor behaves very erratically when blank lines are present. The behaviour is quite weird in general, and the reproducible steps below are just an example.

• Can you reproduce the issue?

Steps to reproduce

1. In a new file, press enter (without shift) a few times to create a few blank paragraphs
2. Type some arbitrary text such as "test"
3. Press shift-enter a few times to create some blank lines
4. Press the up arrow key

Expected behavior:

On pressing the up arrow key, the cursor moves up one line, to the previous blank line.

Actual behavior:

The cursor jumps all the way up to the previous paragraph, above the "test" text that was inserted. If there is no previous paragraph (e.g. if you skip step 1 above) then the cursor does not move at all.

In addition to this, the second time you press shift-enter, nothing seems to happen, so you have to press shift-enter n+1 times if you want to insert n blank lines, unless n=1.

Link to an example: [optional]

Versions

• MarkText version: 0.17.1
• Operating system: Macos 10.15.7

No source file or test is named in the issue. Reproduce the arrow-key and Shift-Enter cases in MarkText 0.17.1 on macOS, then trace the editor's cursor handling; done when blank-line navigation moves one line at a time and inserting n blank lines requires n Shift-Enter presses.