Transferable SSOM Skills for CSOM – CAML
In addition to the names of the main objects in SharePoint’s class hierarchy, there are lots of other pieces of Server-Side knowledge you can bring to Client Side SharePoint Development.
One such example is CAML – or Collaborative Application Markup Language.
In SharePoint Online and CSOM development, you still use CAML for querying lists and defining Lists and Columns.
Although Solutions and the Feature Framework are de-emphasised nowadays, CSOM allows you to create List Columns and Site Columns by invoking AddFieldAsXml, and passing in a string of CAML.
You can also add Lists with a custom Schema, by setting the CustomSchemaXml property on your ListCreationInformation object.
Once again, this is just a string of CAML.