In the 1.0/2.0 version of F+O, section 1.4, it is stated:

"In some cases, the static type returned by a function depends on the type(s) of its argument(s). These special functions are indicated by using bold italics for the return type."

This sentence remains in the current draft of 1.1, but the convention is no longer used, and the markup used to control it has disappeared from the source as an accident of the editorial conversions applied. 

It would be fairly easy to reinstate this, however:

(a) the information is no longer relevant if we are dropping the formal semantics, and

(b) in any case, it violates editorial guidelines to have information in the published specification that is conveyed only by the choice of font.

Subject to the approval of the WG, the editor therefore proposes to drop this feature:

(i) the above-quoted sentence will be removed

(ii) all references to functions having special static type inferencing rules defined in the formal semantics will be removed. (These generally take the form "For detailed type semantics, see...")