Question: when is a hyphen not a hyphen?
Answer: when it’s an artifact.
As hard and soft hyphens look the same, for sighted readers the consequences of confusing the two are likely to be minimal, if any. But to a screen reader user, a passage of text can be rendered almost unintelligible by the incorrect use of hard hyphens.
Hard hyphens, of course, should be used when the hyphen should always be honoured, such as in the phrase “editor-in-chief”, “left-handed” or “self-assured”. Although NVDA ignores such hyphens, JAWS (out-of-the-box) will announce these phrases as “editor dash in dash chief”, “left dash handed” and so on, which is fine.
However, soft (or “discretionary”) hyphens, which map to Unicode as artifacts and hence are ignored by screen readers, should be used when words need to break across line breaks, for example in multi-column layouts or in narrow table column headers.
Problems arise when typesetters manually insert inappropriate hard hyphens instead of soft hyphens. Screen reader users will then hear dashes inappropriately breaking up words, which can seriously compromise readability.
Fortunately, the problem is easily avoidable. To type a hard hyphen you will typically press the key to the right of the zero key (or if you want a non-breaking hyphen it’s Opt/Alt + Cmd/Ctrl and do the same).
To insert a soft hyphen, simply hold down Shift + Cmd/Ctrl and press the key to the right of the zero key.
Inserting hyphens automatically in InDesign
Even simpler though, is that InDesign will automatically add soft hyphens at line breaks if you enable Hyphenation for the relevant paragraph style (Paragraph Styles, Hyphenation and check the Hyphenate check box).
Understanding the distinction between hard and soft hyphens is just one of many essential typographic skills. Getting it wrong can result in time-consuming and expensive remediation work in Acrobat.