------

\definetextbackground[undeftext][location=text,alternative=1,dash=3,background=,frame=off,voffset=-.5ex]

\starttext
Hello \starttextbackground[undeftext]
world!
\page

bbb.

\page
ccc.
\stoptextbackground
\stoptext

------

Proposed patch:

------

--- tex/texmf-context/tex/context/base/mkxl/anch-pgr.lmt.bak 2021-05-07 12:19:30.951643997 -0500
+++ tex/texmf-context/tex/context/base/mkxl/anch-pgr.lmt 2021-05-07 12:19:44.716693548 -0500
@@ -123,6 +123,9 @@
     local ht    = specification.ht
     local dp    = specification.dp
     -- this is not yet r2l ready
+-- myfix
+realpage=texgetcount("realpageno")
+-- end
     local w = d.shapes[realpage]
     local x, y = getpos()
     if trace_ranges then

------

The module-local variable `realpage` is never changed, which is apparently a bug.

Best,

GOU Lingfeng