updatevars = marking updateable content

   <!--mksite:updatevars--> 
   <!--mksite:noupdatevars--> 

The option can be selected in the sitefile, per default we do update content prefixed with these comment variables. mksite:nocommentvars disables this feature as well.

   input: derived <!--$varname:=--> 2004/04
  output: derived 2004-04-16
 default: derived 2004/04

   input: derived <!--on $varname:=--> 2004/04
  output: derived on 2004-04-16
 default: derived 2004/04

   input: derived <!--on $varname:?--> 2004/04
  output: derived on 2004-0416
 default: derived 2004/04

   input: derived <!--$varname:?--> 2004/04
  output: derived - 2004-0416
  output: derived (2004-0416)
 default: derived  2004/04

This is the preferred method of updating content in the htm file. The comment itself is invisible while a default representation is visible (usually in a similar formatting). The expansion will cut away all text following the comment variable up to the next markup or endofline. That text is replaced with the value of the selected variable. If no variable of such a name exists then nothing is done and the default value persists.

The variant expansions can be selected via "?" after the colon instead of the "=". This syntax derives directly from shell variable name expansion which knows the two variants as well ${varname:=default} and ${varname:?default}. A similar syntax was picked up for the attribvars expansion which update markup attribute text intead of page content text.

The variant expansion scheme has two modes. In the direct variant expansion we pick the same as for the expandvars being hyphenated for toplevel variables ("$title" and "$author") and parenthesed for secondary variables ("$modified" and "$issued"). This is not recommended to be used with modern mksite.sh, and instead prefix the variable name with some whitespace to select the core expansion. (The direct variant expansion is a heritage of simplevars).

The variant expansion scheme with some prefix inside the comment markup does only use the core expansion for variable values. The variant value is internally already (a) lowercased from the original value and (b) any additional markup has been cut out. This core modification of variants is very useful to paste variable values into <title> markups - in those the values are officially marked text content but many browsers will treat it as CDATA thereby showing any markup verbatim instead of interpreting them.