Marks are used to record a position in a file, as the file's buffer is modified so does the position that the mark points to -- a mark will keep pointing at the same character no matter what happens (unless the character is deleted!).
The other good thing about marks is that they point to files not buffers. This means that you can set a mark in a buffer, delete the buffer and then move to the position of the mark, the file will be reloaded and the cursor will point at the original character.
Normally there are three user-accessible marks (4) and one special
auto-mark which is used, amongst other things, to record the "previous"
position of the cursor, allowing you to retrace your last major step.
The commands available on marks are,
auto-mark.
auto-mark.
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