A '+' sign means 'read another line of keywords'. A '+' on line
1 would mean that a second line of keywords should be read in. If that
second line contains a '+', then a third line of keywords will be read
in. Regardless of whether a second or a third line of keywords is read in, the
next two lines would be description lines.
Example of '+' option
RESTART T=4D OPEN(2,2) SHIFT=20 PM3 +
SCFCRT=1.D-8 DEBUG + ISOTOPE FMAT ECHO singlet ROOT=3
Example of data set with three lines of keywords.
Note: This and the previous line are the two lines of description.