<!--
IMPORTANT NOTE:
  on tag pages you CANNOT rely on local page variable such as `hasmath`
  `hascode`, `title` etc as the generation of the tag pages will be triggered
  by different pages each of which will have defined these variables in
  a different ways.
  For tag pages, ALL variables used MUST be
  - global ones (whatever you might have defined in `config`)
  - be tag string (`tag`)
  otherwise you cannot guarantee their content.
  There is one way to bend this: you can use {{fill varname rpath}} t