A letter from the Middle English alphabet, it is generally rendered "g" or "y" but in fact can imply a number of sounds:
- g: as in "go"
- gh: as in "knight" (Syr Gawayn and the Grene Kny3t)
- ch: as in loch (such as the poet La3amon, written Layamon)
- z: as in "wounde3," in "Sir Gawain," written "woundez" in most texts, meaning "wounds"
There is no standard equivalent to this letter in HTML, and so 3 is used, though best if the writer bothers to code it as 3 or 3, as it would appear in print. However, PMDBoi pointed out to me that Unicode does have something close: ʒ --the Unicode extention for the IPA symbols, where it "represents the postalveolar voiced fricative, or the 's' in 'leisure.'"
As for its use as either "g" or "y", just take a look at the John Wyclif w/u and you will see how "y" is used as a "g"--the letters were not yet made distinct.