Trait object syntax + trailing plus

Author: Havvy

src/types.md

@@ -498,6 +498,10 @@ Because captures are often by reference, the following general rules arise:
 
 ## Trait objects
 
+> **<sup>Syntax</sup>**  
+> _TraitObjectType_ :  
+> &nbsp;&nbsp; [_Path_] ( `+` [_Path_] )<sup>\*</sup> `+`<sup>?</sup>
+
 A *trait object* is an opaque value of another type that implements a set of
 traits. The set of traits is made up of an [object safe] *base trait* plus any
 number of [auto traits].
@@ -506,10 +510,10 @@ Trait objects implement the base trait, its auto traits, and any super traits
 of the base trait.
 
 Trait objects are written as the path to the base trait followed by the list
-of auto traits followed optionally by a lifetime bound all separated by `+`. For
-example, given a trait `Trait`, the following are all trait objects: `Trait`,
-`Trait + Send`, `Trait + Send + Sync`, `Trait + 'static`,
-`Trait + Send + 'static`.
+of auto traits followed optionally by a lifetime bound all separated by and
+optionally terminated by  `+`. For example, given a trait `Trait`, the following
+are all trait objects: `Trait`, `Trait + Send`, `Trait + Send + Sync`,
+`Trait + 'static`, `Trait + Send + 'static`, `Trait +`.
 
 Two trait object types alias each other if the base traits alias each other and
 if the sets of auto traits are the same and the lifetime bounds are the same.
@@ -701,3 +705,4 @@ impl Printable for String {
 [object safe]: items/traits.html#object-safety
 [issue 47010]: https://github.com/rust-lang/rust/issues/47010
 [issue 33140]: https://github.com/rust-lang/rust/issues/33140
+[_PATH_]: paths.html