consider xdata in preview

[jspitz]

This is a spin-off of #7378.

Consider the following entries:

@XData{CAT,
  publisher = {Addison-Wesley},
  address   = {Reading, MA},
  series    = {Computers and Typesetting},
}

@Book{Knuth,
  title     = {The {\TeX} Book},
  year      = {1984},
  author    = {Knuth, Donald E.},
  xdata     = {CAT},
  number    = {1}
}

The @xdata content is inherited by any entry that links to it (and comma-separated multiple @xdata entries can be employed as well). This is very useful for recurring multi-field entities such as location/publisher/series.

It would be cool if the preview (both customized entry preview and CSL styles) would take this into account, as they do for crossref fields and @string. Note that for @xdata, all fields are taken as is, so no mapping (title->booktitle etc.) is done.

[jspitz]

Note also that sub-inheritance is possible. Xdata can itself inherit xdata (to infinite degree), so you could have different series xdata entries all linking to a publisher xdata entry, and of course a cross-ref'ed entry could inherit xdata as well.

[Siedlerchr]

Thanks for the suggestion. This also refs the old issue #1044
The field is desribe in http://mirrors.ctan.org/macros/latex/contrib/biblatex/doc/biblatex.pdf at section 3.14.6