Using either 'yes', 'no' or 'whatever', the user will be able to choose
whether to force block sequence items to be indented, to force them not
to be indented, or don't care, respectively.
Previously only comments that were indented like the following content
line were allowed, e.g.:
prev: line:
# commented line
current: line
With this change, such new cases are also allowed:
prev: line
# commented line 1
# commented line 2
current: line
