V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

MML
       Maker Markup Language (FrameMaker)


The Free On-line Dictionary of Computing (30 December 2018):

MML

   Human-Machine Language.

   A language from ITU-T for telecommunications applications.
   It has a complex natural-language syntax.

   [CCITT Recommendations Z.311-Z.318, Z-341, Nov 1984].

   (1995-01-31)