Is your feature request related to a problem? Please describe.

The offset is required for specifying the date of a fossil calibration point, which is a major use-case of BEAST. Currently it is not available in beautier.

Describe the solution you'd like

The create_distr() family of functions should have an argument offset that allows setting the offset.

Describe alternatives you've considered

Editing the XML file afterwards either programmatically or by hand.

Additional context

Since create_distr() functions get used in other contexts besides specifying mrca_prior, it may be that the offset setting doesn't make sense / wouldn't get used in all cases.

Example

Example created using Primates.nex example file of BEAST2:

• Screenshot of setting

• gist with xml