latexCheckOptions: Check whether the options for latex functions have been specified.
Description
Check whether the options for latex functions have been specified.
If any of options()[c("latexcmd","dviExtension","xdvicmd")]
are NULL, an error message is displayed.
Usage
latexCheckOptions(...)
Value
If any NULL options are detected, the invisible text of the
error message. If all three options have non-NULL values, NULL.