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Hi,
The Lua(Meta)TeX manuals talk about ghost nodes. I did not find any information on what that is. Up to now, for all other stuff encountered in the LuaMetaTeX manual that I did not know and wanted to have a rough idea of what it is about, I found the relevant information either in the LuaMetaTeX manual itself, in TeX by Topic, or in the ε-TeX manual. I.e. I found it using the LuaMetaTeX manual itself, or the manuals that were referenced at the beginning of chapter 1 of the LuaMetaTeX manual as important additional material.
The Lua(Meta)TeX manual mentiones that \leftghost and \rightghost come from Aleph. I searched the web quite a bit about Omega and Aleph on that issue, and tried other things, but found nothing of relevance. There is a manual for Omega, but, after conversion from ps to pdf, and opening the pdf with Evince, the search function did not find the phrase 'ghost' in it, either. Omega was to a large extend about supporting scripts and fonts for them and when doing so you sometimes need to indicate the boundry of words or glyph runs (regular tex also has a boundary char in the fonts).
first hit on "omega leftghost" http://torus.math.uiuc.edu/jms/tex2mathml/omega-1.23.4/src/web_omega/omfont.... (thinking of it, i'm not sure if we should keep it because I'm not aware of fonts that have kerns wrt left and right ghist glyphs; we do have a boundary node system instead) Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl -----------------------------------------------------------------