utf8 in edge feature values

When writing a pattern for an edge using utf8 chars in feature value (e.g., P -[ super=Métaphore ]-> Q), a lexing error is raised:

Libgrew.Libgrew.Error("[file: example-1.patt.bad, line: 5] [Grew_loader.Loader.pattern], Lexing
error: unexpected character '\195'")

A workaround is available using instead:

e:P -> Q ;
e.super="Métaphore"