The name of an existing keyword in the FITS extension whose
value is to be reported. 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 existing
keywords.
KEYWORD may have an occurrence specified in brackets []
following the name. This enables the values to be obtained
for keywords that appear more than once. 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 occurrence.
The suggested value is the current value.