Why would you want to do this? Some words bedevil hyphenation engines. For instance,
How do you know whether a word won’t be hyphenated correctly? The problem usually afflicts words that aren’t in a standard hyphenation dictionary, like jargon words, unusual proper names, and other words with nonstandard spellings, like trade names. As former Supreme Court Justice Potter Stewart might have said, you’ll know it when you see it.
s for soft,
hy for hyphen)
Even though you type a key to insert an optional hyphen, you won’t see it until it’s needed. And obviously, if your automatic hyphenation is turned off, you’ll never see it.
For the hyphenation in this book, I used Frank Liang’s hyphenation algorithm to insert optional hyphens when each page is generated. (I’ve released this code as an open-source hyphenation module for Racket.) Though CSS notionally supports hyphenation, it’s not implemented as widely as the optional hyphen.