Clarifying behavior of #[derive(Ord, PartialOrd)] in doc comments.

Removing redundant statement about lexicographic ordering.

src/libcore/cmp.rs

@@ -165,9 +165,8 @@ impl Ordering {
 /// - total and antisymmetric: exactly one of `a < b`, `a == b` or `a > b` is true; and
 /// - transitive, `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.
 ///
-/// When this trait is `derive`d, it produces a lexicographic ordering.
-///
-/// This trait can be used with `#[derive]`.
+/// This trait can be used with `#[derive]`. When `derive`d, it will produce a lexicographic
+/// ordering based on the top-to-bottom declaration order of the struct's members.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait Ord: Eq + PartialOrd<Self> {
     /// This method returns an `Ordering` between `self` and `other`.
@@ -225,7 +224,8 @@ impl PartialOrd for Ordering {
 /// total order. For example, for floating point numbers, `NaN < 0 == false` and `NaN >= 0 ==
 /// false` (cf. IEEE 754-2008 section 5.11).
 ///
-/// This trait can be used with `#[derive]`.
+/// This trait can be used with `#[derive]`. When `derive`d, it will produce an ordering
+/// based on the top-to-bottom declaration order of the struct's members.
 #[lang = "ord"]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {