So in the documentation they had

1.9 Ext4 file system parameters
------------------------------

As you can see the 's' doesn't get a '-' under it. So they changed the documentation to:

1.9 Ext4 file system parameters
-------------------------------

so the 's' in parameters gets a dash under it.

this seems to be the standard as everywhere else the dashes go for the same length of characters as the above line. Example:

2.0 /proc/consoles
------------------

The little girl said the 's' in parameters is sad because it didn't get the dash under it and it was all alone. So they added the dash.