Superscript in \markup environment

[Robert Blackstone]

Dear list

The LilyPond-project that I'm presently working on deals with some 40 songs, 
voice and a keyboard instrument, with comments and explanations underneath each 
score, some with small musical examples.
In these comments I would like interval names like 5ths and 8ves to be written 
with "ths" and "ves" as superscript, but up till now none of superscript 
possibilities I found in the LilyPond Notation Reference worked in the 
\markup -part of the file. They sometimes even made the whole comment disappear.

 See the MWE below. (not so minimal, my apologies). What can I do to get these 
superscripts?
(Both the music and the comment are fictional. Just found some snippets that 
could serve my purpose here.)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\version "2.18.2"

\relative c' 
{ 
\new Staff { \omit Staff.TimeSignature \clef treble \time 3/2
<<  
{\stemUp cis'2 \once \hideNotes  b4 \once \hideNotes b b2 }\bar "||" 
\new Voice {\voiceTwo \stemDown  a2 \set fontSize = #-4 \single \hide Stem gis4 
\single \hide Stem fis4^- \unset fontSize e2 |} 
>>
<<  
{\stemUp fis2 \once \hideNotes r4 \once \hideNotes r4 e2 } \bar "||" 
\new Voice {\voiceTwo \stemDown d2 \set fontSize = #-4 \single  \hide Stem cis4 
 \single \hide Stem b4^-  \unset fontSize a2 |} 
>>
}\bar "||"

}
}
}
    
 \markup {
\fill-line {" "
{
\column {
\left-align {
"Sometimes hidden parallel 5ths can be tolerated but these could have been 
avoided by contrary movement." "The same goes for parallel 8ves."

    } %end left-align
    } %end Column
    }
    } % end fill-line
    } %end markup
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


Thanks in advance for any advice.

Kind regards,
Robert Blackstone