You may be familiar with the two different approaches to grammar known as descriptive and prescriptive grammar. The Concise Oxford Companion to the English Language defines these approaches as follows:
A descriptive grammar is an account of a language that seeks to describe how it is used objectively, accurately, systematically, and comprehensively. A prescriptive grammar is an account of a language that sets out rules (prescriptions) for how it should be used and for what should not be used (proscriptions), based on norms derived from a particular model of grammar. (p 262-63)
A way to illustrate this is that a descriptivist would include “aint” in the dictionary because it is a word that people say, while a prescriptivist would not include it because it is a vulgar word, or a neologism and so should not be included.
I think the same schools of thought can be helpfully applied to the term “Anglicanism” today. Just what does it mean to be Anglican? If we use the descriptivist approach, we come up with an answer so broad as to cease being useful. You can be homosexual, bow to man-made objects, pray to Mary and the saints, be a conservative evangelical, be an Arminian or Calvinist, be charismatic or cessationist, and on and on. Archbishop Orombi attempted a summary a few years ago (here). There really aren’t many boundaries at all, everyone claims a right to the title and most have at least some historical precedent for their position.
If we turn to prescriptivist approach, I think we can fairly establish the parameters by looking at the two foundings of Anglicanism as something unique – the first under Henry VIII and the second under Elizabeth, the Virgin Queen. We could look at the formularies of the Church, the substance of the Book of Common Prayer, the Book of Homilies, the writings of the early Bishops and clergy, and so on. Although there will not be complete unity from this body of literature, I believe that there is enough substance to establish a firm baseline for what “Anglicanism” was intended to be.
Unfortunately, as Nietzsche said, the “world is the will to power” and the trajectories of Anglicanism show this in practice. Folks have paid no heed to the genesis of Anglicanism and have made it into a multifarious mess. As a prescriptivist I cannot agree that their interpretations are valid, ultimately they fail the Scriptural test. But from a descriptivist perspective, they can only be called Anglicans because that is what they call themselves.
Here are some sources that can contribute to a better understanding of what Anglicanism was intended to be:
 The Doctrine of the Church of England as to the Effects of Baptism in the Case of Infants, by William Goode.
 The Primer: a Book of Private Prayer, edited by Henry Walter.
 Eighteen Sermons Preached in Oxford 1640, by Archbishop James Usher.
 The Principal Ecclesiastical Judgments Delivered in the Court of Arches 1867 to 1875, by Sir Robert Phillimore.
 Certain Sermons or Homilies: Appointed to be Read in Churches in the Time of the Late Queen Elizabeth, by the Church of England.
 Lives of the Elizabethan bishops of the Anglican Church, by Francis Overend White.
 Formularies of faith put forth by authority during the reign of Henry VIII, ed. Charles Lloyd
 The Ecclesiastical Law of the Church of England, Sir Robert Phillimore
And of course, Richard Hooker’s Laws of Ecclesiastical Polity, all the works of Latimer, Cranmer, and Jewel.