A space, not a non-breaking space, just an ordinary space. Can't be that hard, can it? Well, you would think so. Or I'm rubbish at googling the right thing.
I was working on a project at work, and adding schema.org markup which involved wrapping stuff in
<span>s. Which in turn choked my HTML minifier and caused one particular space to disappear. Took me ages to find the solution; how to actually insert an entity for a space.
yup 32, those of us who are old enough remember 32 is the ASCII code for a space. Obvious, eh?