CAML is the XML definition for all things in SharePoint, in deployment, and in creating templates, CAML is the only format. In SharePoint development, you will also need to know CAML, in particular, how to write a query in CAML.
More info: Introduction to Collaborative Application Markup Language (CAML) and Query Schema
<query><orderby><fieldref name="Modified" ascending="FALSE"></fieldref></orderby><where><and><neq><fieldref name="Status"></fieldref><value type="Text">Completed</value></neq><isnull><fieldref name="Sent"></fieldref></isnull></and></where></query>
Figure: Example of CAML query
You can see - CAML is essentially the same as SQL WHERE syntax, but wrapped in an XML format.
Problems with CAML:
<Query><Where><Or><Eq><FieldRef name="Status" /><Value Type="Text">Completed</Value></Eq><IsNull><FieldRef Name="Status"></IsNull></Or></Where></Query>
Figure: Example of CAML query
❌ Figure: Debug error message
Tip: Use 3rd Party tools - U2U CAML Query Builder
✅ Figure: U2U CAML Query Builder
Note: U2U CAML Builder is the best tool that we have. There are some occasional UI and interface issues, but for creating CAML and testing it against live SharePoint lists it gets the job done. And it’s free!