Controlling the order of articulations and text markup

[Richard Shann]

I am having trouble controlling the stacking order of articulations and
text. Sometimes in musical scores two ornaments are placed one above the
other and I can't find documentation to say how the vertical order of
the ornaments can be controlled. Sometimes I create ornaments using
markup via \epsfile, and again I would like to be able to control the
order of these amongst ordinary ornaments.

Here is an example ("Text" here stands in for some \epsfile ornament)

\version "2.18.2"
{
%\once \override TextScript.outside-staff-priority = #450  
%\once \override Script.outside-staff-priority = #450  

c''  ^Text ^\turn ^\prall
}

In the comments are two possible controlling statements - the TextScript
one is documented as setting the priority of the Text, the other I have
made up based on the documentation for articulations such as \turn,
however, it seems these are different beasts in some way and the
construct may simply be wrong. #450 is the default priority of
TextScript, but articulations don't appear in the table at
http://www.lilypond.org/doc/v2.18/Documentation/learning/outside_002dstaff-objects
because presumably they aren't "outside-staff-objects"
To add to my confusion, at
http://www.lilypond.org/doc/v2.18/Documentation/notation/expressive-marks-attached-to-notes#articulations-and-ornamentations
I find the following suggestion for modifying the order of text scripts:

\once \override TextScript.script-priority = #-100

The bottom line is - I would like a general way of controlling the
position of ^Text ^\turn ^\prall in the above example. Anyone able to
help?

Richard Shann