To create two or more `first' or header lines for a definition, follow
the first @deffn line by a line beginning with @deffnx.
The @deffnx command works exactly like @deffn
except that it does not generate extra vertical white space between it
and the preceding line.
For example,
@deffn {Interactive Command} isearch-forward
@deffnx {Interactive Command} isearch-backward
These two search commands are similar except ...
@end deffn
produces
Interactive Command: isearch-forward
Interactive Command: isearch-backward
These two search commands are similar except ...
Each of the other definition commands has an `x' form: @defunx,
@defvrx, @deftypefunx, etc.
The `x' forms work just like @itemx; see section @itemx.