Something
public text v1 · immutable Alias /trac "/usr/share/trac/htdocs"
<LocationMatch "/.+/projects">
SetHandler mod_python
PythonHandler trac.web.modpython_frontend
PythonOption TracEnvParentDir /home/trac/projects
PythonOption TracUriRoot /projects
</LocationMatch>
<LocationMatch "/.+/projects/$prjname">
SetHandler mod_python
PythonHandler trac.web.modpython_frontend
PythonOption TracEnvParentDir /home/trac/projects/$prjname
PythonOption TracUriRoot /projects/$prjname
</LocationMatch>