Dear All 
 Unable to compile metafun manual with current release of LMTX for linux X86_64 and  RPI 4 (both Raspberry PI OS 32 bit and Manjaro Linux ARM 64). engine: luametatex version: 2.0802, functionality level: 20201118 

tex error       > tex error on line 240 in file metafun-positioning.tex: Missing number, treated as zero.   This problem never occurred in earlier compilations with LMTX. 

Commenting out  file metafun-positioning.tex  metafun  manual compiles successfully.  Same problem is exhibited in different version of ubuntu and arch linux X86_64  , 

Thank you all for your feedback. 

Giulio B. 

234     \startsection[title={A more detailed view}]  

235  

236     As we know, a decent portion of \TEX's attention is focused on breaking  

237     paragraphs into lines and determining the optimal point to split off the page.  

238     Trying to locate the optimal points to break lines is a dynamic process. The  

239     space between words is flexible and we don't know in advance when a \hpos {A-1}  

240 >>  {word} or piece of a word |<|maybe it's best to talk of typographic \hpos {A-2}  

241     {globs} instead|>| will end up on the page. It might even cross the page  

242     boundary.  

243  

A number should have been here; I inserted '0'. (If you can't figure out why I  

needed to see a number, look up 'weird error' in the index to The TeXbook.)  

  mtx-context     | fatal error: return code: 256