[Therion] Metapost snippets out-source-able from thconfig/layout?

[Christian Rößler (Roessler)]

Hallo everybody,

due to learning some metapost for making a Schacht (shaft?) symbol, I got 
a thconfig file getting really fat and difficult to maintain. Is there a 
possibility to source metapost snippets from another file?

Neither 'source' nor 'input' (Handbook p. 15) seem to work, which does not 
wonder me as the context 'layout' has to be obeyed.

So, how are the people here handling that? Big, fat thconfig, or is there 
another way?

Best regards, Christian