The name of the keyword whose existence in the FITS extension
is to be tested. A name may be compound to handle hierarchical
keywords, and it has the form keyword1.keyword2.keyword3
etc. The maximum number of keywords per FITS card is 20.
Each keyword must be no longer than 8 characters, and be a
valid FITS keyword comprising only alphanumeric characters,
hyphen, and underscore. Any lowercase letters are converted to
uppercase and blanks are removed before comparison with the
KEYWORD may have an occurrence specified in brackets 
following the name. This enables testing for the existence of
multiple occurrences. Note that it is not normal to have
multiple occurrences of a keyword in a FITS header, unless it
is blank, COMMENT or HISTORY. Any text between the brackets
other than a positive integer is interpreted as the first
The suggested value is the current value.