HTCondorWiki: Adding Metaknobs

 As of 8.5.6 metaknobs can have arguments, which opens exciting new possibilities.
 see https://htcondor-wiki.cs.wisc.edu/index.cgi/tktview?tn=5739,0
 
+In metaknob statements any $(arg) where arg starts with a digit will be substituted as the *use* line is parsed. (valid param names can't start with a digit). The substitutions are
+
+*: =$(0)= all of the args
+*: =$(0?)= 1 if any arguments, 0 if no arguments
+*: =$(0#)= the number of arguments (i.e. the number of commas+1)
+*: =$(1)= the first argument
+*: =$(1?)= 1 if the first argument is non-empty, 0 if it is empty
+*: =$(1+)= all of the arguments, starting with the first one. equivalent to =$(0)=
+*: =$(2)= the second argument
+*: =$(2?)= 1 if the second argument is non-empty, 0 if it is empty
+*: =$(2+)= all of the arguments, starting with the second one
+*: =$(3)= the third argument
+*: etc
+
 For instance. The =FEATURE : PerodicCronHook= metaknob is declared thus:
 
 {snip: from param_info.in}
@@ -24,5 +38,13 @@
      $(1)_$(2)_ARGS=$(5)
    endif
 @end
+{endsnip}
+
+And the =FEATURE : StartdCronPeriodic= metaknob uses it. it is declared
+{snip: from param_info.in}
+[$FEATURE.StartdCronPeriodic]
+friendly_name=Configure a STARTD Cron periodic Hook, args: tag, period, exe [, hook_args]
+default = use FEATURE : PeriodicCronHook(STARTD_CRON, $(0))
+{snip}
 
 {endsnip}