How to "Set previous context mark"?

Question

From the vim manual:

m'  or  m`      Set the previous context mark.  This can be jumped to
            with the "''" or "``" command (does not move the
            cursor, this is not a motion command).

I could not understand what this does or what its used for, tried to "set" previous mark to another mark using that, but it did not work.

Answer 1

The ' and ` are synonymous. It correspond to position before the last move (with the exception of the very small moves. e.g. one character, one line)

The m' (and its sister: m`):

• Set the last position mark explicitly
• Add an entry at the top of jump list
• Move the jump list cursor to the to of the it

I believe this command is used by plugin developers when they create moves.

It let them:

• Mark the original position before the jump
• Maintain the jump list

This to make the jump commands works like expected:

• Ctrlo
• Ctrli
• ''
• `'