Scale domain should accept array of datarefs about vega

[jheer]

Yes, this would certainly be useful! You can approximate some of this functionality using separate domainMin and domainMax specifications, but this (unhelpfully) requires knowing in which data sets your extrema lie. I'll add this to the feature request list for future versions. In the meantime, pull requests implementing this feature will be given due consideration!

[jheer]

Multi-doman scale support was added in commit a19dc3e. To use multiple domains pulling from different data sets, use the following syntax:

"domain": {"fields": [
  {"data": "table1", "field": "data.field1"},
  {"data": "table2", "field": "data.field2"}
]}