The warnings are great but it's hard to tell where they might be coming from. Patch attached to emit source file names for errors
- creates an 'InitialRenderContext instead of just a RenderContext, and uses that to initialize the DocEngine so properties are always available.
- adds "sourceFile" property to context and updates for each file being rendered
- adds 'emitWarning' for consistent messages
- uses constants for context property keys
- removes custom configureContext field from DocEngine