Why do I receive the message that my "content model is non-deterministic (ambiguous)"?

Why do I receive the message that my "content model is non-deterministic (ambiguous)"?

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Article ID: KB0087837

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Updated On:

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Description

Resolution:
The XML 1.0 specification requires that content models be deterministic, or unambiguous. Examples of ambiguous content models include:
((a , b) | (a , c))
(a?, b?, a*, c?)
In each case, given an initial occurrence of "a", the XML processor cannot know which "a" is being used.  Because many DTD parsers do not perform a determinism check, this check can be turned off in XML Authority (Edit>&gtPreferences).

Issue/Introduction

Why do I receive the message that my "content model is non-deterministic (ambiguous)"?