In 2.2.1 appears the following:
"The term CSS element reference identifier is used as defined in the CSS Image Values and Replaced Content specification to define the API that declares identifiers for use with the CSS 'element()' function. [CSSIMAGES]"
However, the term "CSS element reference identifier" is never used in the current draft of HTML5; therefore, this paragraph should be removed.
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Change Description: https://github.com/w3c/html/commit/bbe9778e852aa39928038a1d8d1298f3bab7146e
Rationale: Unused term removed from the spec.