My assumption was that the purpose of this soft hyphen would be to
mark a visible hyphen or dash character that can be used as a word
separator; for example, in order to break the word "drawing-
parlour" at a margin (as in this letter), one would use the string
"drawing­parlour" in their HTML document.
The other interpretation is that ­ would mark an *invisible*
point at which a word can be broken; thus, "al­go­rithm"
could be used to represent a word which can be broken at a margin
into the portions "al-" and "gorithm," or "algo-" and "rithm,"
depending on which is needed by the browser.
Which is the intended usage?
If the former, I will suggest again that perhaps the recommended
behavior for browsers should be to interpret a minus character as a
soft hyphen, and to introduce an entity for the hard hyphen and the
minus character, on the basis that the minus is more often used in
the role of a soft hyphen than in the other two roles. (And, again,
if this suggestion violates a fundamental tenet of SGML or HTML of
which I am not aware, then I respectfully retract this suggestion.)