model.field(<tag>).shape(<shlist>) sets the shape functions defining the field variables.
<shlist> is a list of shape function tags. Each shape function defines one or more field variables. Together the shape functions specify which field variables there are in the field.
model.field(<tag>).field() returns the field name as a string.
model.field(<tag>).shape() returns the shape function tags as a string array.
model.field(<tag>).geom() returns the geometry associated with the field.