To typeset beams grouped 3-4-3-2 in 12/8 it
is necessary first to override the default beam endings
in 12/8, and then to set up the new beaming endings:
Text crescendi (or decrescendi, ritardandi, etc.) show a dashed line by default. To hide this spanner line, simply set the dash-period of DynamicTextSpanner (or TextSpanner if you use one for rit.) to a negative value.