Apply suggestions from code review

Co-Authored-By: Mazdak Farrokhzad <[email protected]>

Author: RalfJung

src/behavior-considered-undefined.md

@@ -44,15 +44,15 @@ code.
   * A `!` (all values are invalid for this type).
   * [Uninitialized memory][undef] in the value of an integer (`i*`/`u*`),
     floating point value (`f*`), or raw pointer.
-  * A dangling or unaligned reference or `Box`, or one that points to an invalid value.
+  * A reference or `Box<T>` that is dangling, unaligned, or points to an invalid value.
   * Invalid metadata in a wide reference, `Box`, or raw pointer:
     * `dyn Trait` metadata is invalid if it is not a pointer to a vtable for
-      `Trait` that matches the actual dynamic trait the reference points to.
+      `Trait` that matches the actual dynamic trait the pointer or reference points to.
     * Slice metadata is invalid if if the length is not a valid `usize`
       (i.e., it must not be read from uninitialized memory).
   * Non-UTF-8 byte sequences in a `str`.
   * Invalid values for a type with a custom definition of invalid values, such
-    as a `NonNull` that is null. (Requesting custom invalid values is an
+    as a `NonNull<T>` that is null. (Requesting custom invalid values is an
     unstable feature, but some stable libstd types, like `NonNull`, make use of
     it.)
 
@@ -67,7 +67,7 @@ points to are part of the same allocation (so in particular they all have to be
 part of *some* allocation). The span of bytes it points to is determined by the
 pointer value and the size of the pointee type. As a consequence, if the span is
 empty, "dangling" is the same as "non-null". Note that slices point to their
-entire range, so it is very important that the length metadata is never too
+entire range, so it is important that the length metadata is never too
 large. In particular, allocations and therefore slices cannot be bigger than
 `isize::MAX` bytes.