⌂ Printing both the ancient and the modern clef in vocal music

Until the late 17th century, vocal parts were printed using specific clefs for each voice. In modern editions, the modern clef is printed but sometimes it is preceded by the traditional clef. Here is how to achieve it in LilyPond: you have to replace the clef symbol by a \markup block, and that can only be done by overriding the 'stencil property to make it print a text element. Then you have to define this text element as a markup, and insert in it the \musicglyph you need. Notice the \raise command: it is used to place the C clef properly on the staff.