How to include HTML entities into an XML file

[Spy520]

In firefox :\[code\]<?xml version="1.0" encoding="utf-8"?><math display="block" xmlns="http://www.w3.org/1998/Math/MathML"> <mi>&rho;</mi></math>\[/code\]results in "undefined entity" error.I know there is something missing there. I just don't know what I should write to correct the problem. I would like to avoid rewriting every single unicode character into the document.EDIT I tried the following, still not working, same error :\[code\]<?xml version="1.0" encoding="utf-8"?><!DOCTYPE math [ <!ENTITY % HTMLlat1 PUBLIC "-//W3C//ENTITIES Latin 1 for XHTML//EN" "xhtml-lat1.ent"> %HTMLlat1; <!ENTITY % HTMLsymbol PUBLIC "-//W3C//ENTITIES Symbols for XHTML//EN" "xhtml-symbol.ent"> %HTMLsymbol; <!ENTITY % HTMLspecial PUBLIC "-//W3C//ENTITIES Special for XHTML//EN" "xhtml-special.ent"> %HTMLspecial;]><math display="block" xmlns="http://www.w3.org/1998/Math/MathML"> <mi>&rho;</mi></math>\[/code\]EDIT In chrome, this results in the following message :\[code\]error on line 6 at column 13: PEReference: %HTMLlat1; not foundwarning on line 10 at column 15: PEReference: %HTMLsymbol; not foundwarning on line 14 at column 16: PEReference: %HTMLspecial; not found\[/code\]EDIT Tried to download the .ent files and change the reference to either a local http:// path or file:/// path with no success.A similar post about the subject : XML catalog in PHP