DiffEqPDEBase.jl is a component package in the DiffEq ecosystem. It holds the common types and utility functions which are shared by other component packages which are related to solving PDEs in order to reduce the size of dependencies. Additionally, this package holds tools for creating unstructured finite element meshes to be used in component solver packages. Users interested in using this functionality in full should check out DifferentialEquations.jl
The documentation for the interfaces here can be found in DiffEqDocs.jl and DiffEqDevDocs.jl. Specific parts to note are: