Add a comment about hasvalue/getvalue

Author: mhauru

src/varnamedvector.jl

@@ -1187,6 +1187,9 @@ function values_as(vnv::VarNamedVector, ::Type{D}) where {D<:AbstractDict}
     return ConstructionBase.constructorof(D)(pairs(vnv))
 end
 
+# See the docstring of `getvalue` for the semantics of `hasvalue` and `getvalue`, and how
+# they differ from `haskey` and `getindex`. They can be found in src/utils.jl.
+
 # TODO(mhauru) This is tricky to implement in the general case, and the below implementation
 # only covers some simple cases. It's probably sufficient in most situations though.
 function hasvalue(vnv::VarNamedVector, vn::VarName)