Existing Wording: Before reading this implementation guide, its important to be familiar with some of the basic principles of FHIR as well as general guidance on how to read FHIR specifications.

Proposed Wording: Before reading this implementation guide, it is important to be familiar with some of the basic principles of FHIR as well as general guidance on how to read FHIR specifications.

Comment:

Make "its" to "it is"

Summary:

"its" was not grammatically correct in this sentence. It is suggested that the author use "it is".