"Meta-Languages and Semantics for Equation-Based Modeling and Simulation"
    David Broman
    "Modeling Kernel Language" thesis, also a bunch of Modelica

"Modelyze: a Gradually Typed Host Language for Embedding Equation-Based Modeling Languages"
    David Broman and Jeremy G. Siek
    modelyze tool is successor to MKL

Modelica Spec
    PDF or http://modelica.readthedocs.io/

µ-Modelica Language Specification

"Modelica by Example"
    http://book.xogeny.com/

"Introduction to the Dynamic Modelling of Thermo-Fluid Systems using Modelica"
    "minicourse"
    http://staff.polito.it/roberto.zanino/sub1/teach_files/modelica_minicourse/index_modelica.html
    eg, "Properties of Differential-Algebraic Equation Systems (DAE)" (slides)