LATERAL synopsis

On the SELECT manual-page synopsis,

http://www.postgresql.org/docs/devel/static/sql-select.html

the LATERAL feature is documented in three sparate lines (the are separate, right?). Because of
their length I was going to reformat them to let them fit in the .PDF page format, but looking a
bit closer at that synopsis I have to admit I don't really understand it. Could someone please
explain?

[ LATERAL ] ( select ) [ AS ] alias [ ( column_alias [, ...] ) ]

and:

[ LATERAL ] function_name ( [ argument [, ...] ] ) [ AS ] alias [ ( column_alias [, ...] |
column_definition [, ...] ) ]

and:

[ LATERAL ] function_name ( [ argument [, ...] ] ) AS ( column_definition [, ...] )

All three are listed as possible 'from_item's.

But what does 'column_definition' stand for? (These are the only occurrences of
'column_definition' in the manual.)

Are not the first two of the above LATERAL-lines sufficient? Or perhaps it would be even better
to reduce it to only the first of those three lines (i.e. get rid of the 'function_name' lines)?

Thanks,

Erik Rijkers