* Update helpcontent2 from branch 'master'
  - tdf#121084 Help page for Calc REGEX function
    
    * honor DTD
    * follow erAck advise
    
    Change-Id: Ib911888fbc5aae9c4a749c9343218081df9f6783
    Reviewed-on: https://gerrit.libreoffice.org/63430
    Tested-by: Jenkins
Reviewed-by: Eike Rathke <erack@redhat.com>