First, I use a font called "Migu 2M" in Emacs.
When I run M-x htmlfontify-buffer in one buffer, the exported HTML contains lines like:
```
body, pre { text-decoration: none; font-family: Migu 2M; font-stretch: normal; font-weight: 500; font-style: normal; color: #ffffff; background: #000000; font-size: 15pt; }
```
Standards-compliant web browsers should ignore this font-family.
MDN Web Docs says:
> Valid family names
> Font family names must either be given quoted as strings, or unquoted as a sequence of one or more identifiers. This means that punctuation characters and digits at the start of each token must be escaped in unquoted font family names.
>
> It is a good practice to quote font family names that contain white space, digits, or punctuation characters other than hyphens.
An unquoted font-family is valid as long as it doesn't start with a digit, but MDN Web Docs also says:
> The following example is technically valid but is not recommended:
> font-family: Gill Sans Extrabold, sans-serif;
So it makes sense to quote all font-family.
The attached patch file fixes that issue. Thank you for reading.