
The tt(STARTDEF) macro typically occurs in files that define a macro package
for Yodl. The macro signals the tt(yodl) program that the following input holds
only the definitions of macros, symbols etc..

When tt(yodl) is inside a definition, the generation of empty lines on the
output is suppressed, and tt(yodl) warns when non-whitespace output is
generated. Using tt(STARTDEF) is never obligatory, but it is useful in a macro
file. Macro files tend to define a lot of symbols or commands, leading to
unnecessary spaces and newlines.

The definition section is ended with the tt(ENDDEF) macro. 

Example:

verb(\
STARTDEF()

DEFINESYMBOL(....)
DEFINEMACRO(...)(...)(...)

ENDDEF())

Without the tt(STARTDEF) and tt(ENDDEF), the above definition would generate
four empty lines in the output.
