I think this paragraph (in Mandatory Values section) is misleading:

Two of the values in font shorthand are mandatory: font-size and font-family. If either of these is not included, the entire declaration will be ignored.

Because some keywords will work, for example:

p {
  font-weight:bold;
  font-size: 3em;    
  font: inherit;
}

In the rule above, the third declaration is not ignored. To the contrary, it will reset the font-weight and font-size declarations.

See Section 15.8 Shorthand font property.

However, because we’ve redeclared the font property on the paragraph elements, all the optionals will be reset on the paragraphs, causing the style, variant, weight, and line-height to revert to their initial values.

Would something along the lines of font: 30px/inherit Georgia, sans-serif; fix this in terms of the line-height at least?