outside-staff-priority for markups attached to <>

[Richard Shann]

When I generate text to appear above some music using the <>^\markup
"mytext" syntax, I don't seem to be able to control the
outside-staff-priority. In this example despite the second bit of markup
having a lower outside-staff-priority it appears above the first bit.

\version "2.18.0"
\score {
 {  \once \override TextScript.outside-staff-priority = #1000  <> ^\markup 
"Above the next text please" 
     \once \override TextScript.outside-staff-priority = #0  a'4^"below please"
 }
}


Can anyone suggest why this is happening and if there is a solution that
doesn't involve using a different sort of syntax for the markup, (i.e.
not involving the <> trick)? (The final target of all this is scores
with markup containing encapsulated postscript to create old French
clavecin ornaments which have to have a low outside-staff-priority
despite being textScript).

Richard Shann