When DITA2Go encounters a cross reference, index term, or footnote reference in a context where an <xref> tag would be invalid, the <xref> gets wrapped in a <ph> element. These DITA2Go-generated <ph> wrapper elements need an outputclass attribute. The default outputclass attribute names for cross-reference, index-term, and footnote wrappers are as follows:
[DITAOptions]
; XrefWrapClass = outputclass to use for generated ph elements that
; wrap xrefs where they would otherwise be invalid
XrefWrapClass = phxref
; IndexWrapClass = outputclass to use for generated ph elements that
; wrap indexterms where they would otherwise be invalid
IndexWrapClass = phindex
; FootnoteWrapClass = outputclass to use for generated ph elements
; that wrap footnotes where they would otherwise be invalid
FootnoteWrapClass = phfoot