'h' and 'l' move the cursor by "modifier" characters. 'j' and
'k', by lines.

'H' goes to the beginning of the line, 'L' to the end.

'w' moves forward by "modifier" words. 'b' moves backward.
'W' moves to end-of-word. 'B', backwards.

'I', 'F', 'Y', 'X' and 'E' invoke the corresponding command
from the Block Editor (B100). Refer to documentation there.

'o' inserts a blank line after the cursor. 'O', before.

'D' deletes "modifier" lines at the cursor. The first of those
lines is copied to IBUF.
                                                        (cont.)