What does that even mean?!
It goes back to the conditions of the Church of England in the 16th century. Queen Elizabeth guided the church between the extremes of the hardline Catholics and Puritans and thereby avoided civil war. It was called the Elizabethan Settlement, a sort of compromise between Catholicism and Protestantism. Comprehensiveness came to mean a church that could accomodate both high and low church factions, in other words a broad, two-party church. And Anglicans have traditionally taken some pride and satisfaction in this comprehensiveness, embracing tolerantly and concurrently what they thought to be the best of Catholic and Protestant theology and practice.
However, over the part 40 years, the term "comprehensivenes" has become a cliche to cover all sorts of goofy ideas coming from the political left in the church. So if a conservative disagrees about leftist ideas coming into the church, the left starts talking about a tradition of comprehensiveness. It has become a meaning less term.