From HTML WG Wiki
In September of 2002, an "HLink" draft was published by the W3C HTML Working Group, signaling a rift that is significant in the history of HTML in that it was a key indicator that some W3C recommendations for XML-based technologies might be out of sync with Web realities and that is foreshadowed a similar rift that would take place later with regard to XForms
XLink had been developed as a generic and more powerful replacement to the simple linking mechanism (the a element) in HTML 4.01, with the expectation that XLink would be adopted in all future W3C specifications that required a linking mechanism. HLink was developed and published by the third W3C HTML Working Group (then working on XHTML 2.0) for use in XHTML 2.0 -- only after members of the group had repeatedly made it clear that certain problems with XLink prevented it from meeting their requirements, and only after those problems they pointed out were never addressed.
The W3C TAG ended up unamimously ruling that "XLink should be used for hypertext references in XHTML 2.0", and Steven Pemberton (the chair of the fourth W3C HTML Working Group, then working on XHTML 2.0) responded to say:
That the TAG doesn't yet understand how XLink gets in the way of combining with other specifications will be the source for much future discussion.