Added "of" to "objective functions is that they consist of two parts" in line 32 of ./doc/tutorials/model.rst
The documentation of xgboost is generated with recommonmark and sphinx. You can build it locally by typing "make html" in this folder. Checkout https://recommonmark.readthedocs.org for guide on how to write markdown with extensions used in this doc, such as math formulas and table of content.