Document the Tm struct and fields

src/libtime/lib.rs

@@ -187,20 +187,51 @@ pub fn tzset() {
     }
 }
 
+/// Holds a calendar date and time broken down into its components (year, month, day, and so on),
+/// also called a broken-down time value.
 #[deriving(Clone, Eq, Encodable, Decodable, Show)]
 pub struct Tm {
-    tm_sec: i32, // seconds after the minute ~[0-60]
-    tm_min: i32, // minutes after the hour ~[0-59]
-    tm_hour: i32, // hours after midnight ~[0-23]
-    tm_mday: i32, // days of the month ~[1-31]
-    tm_mon: i32, // months since January ~[0-11]
-    tm_year: i32, // years since 1900
-    tm_wday: i32, // days since Sunday ~[0-6]
-    tm_yday: i32, // days since January 1 ~[0-365]
-    tm_isdst: i32, // Daylight Savings Time flag
-    tm_gmtoff: i32, // offset from UTC in seconds
-    tm_zone: ~str, // timezone abbreviation
-    tm_nsec: i32, // nanoseconds
+    /// Seconds after the minute – [0, 60]
+    tm_sec: i32,
+
+    /// Minutes after the hour – [0, 59]
+    tm_min: i32,
+
+    /// Hours after midnight – [0, 23]
+    tm_hour: i32,
+
+    /// Day of the month – [1, 31]
+    tm_mday: i32,
+
+    /// Months since January – [0, 11]
+    tm_mon: i32,
+
+    /// Years since 1900
+    tm_year: i32,
+
+    /// Days since Sunday – [0, 6]. 0 = Sunday, 1 = Monday, …, 6 = Saturday.
+    tm_wday: i32,
+
+    /// Days since January 1 – [0, 365]
+    tm_yday: i32,
+
+    /// Daylight Saving Time flag.
+    ///
+    /// This value is positive if Daylight Saving Time is in effect, zero if Daylight Saving Time
+    /// is not in effect, and negative if this information is not available.
+    tm_isdst: i32,
+
+    /// Identifies the time zone that was used to compute this broken-down time value, including any
+    /// adjustment for Daylight Saving Time. This is the number of seconds east of UTC. For example,
+    /// for U.S. Pacific Daylight Time, the value is -7*60*60 = -25200.
+    tm_gmtoff: i32,
+
+    /// Abbreviated name for the time zone that was used to compute this broken-down time value.
+    /// For example, U.S. Pacific Daylight Time is "PDT".
+    tm_zone: ~str,
+
+    /// Nanoseconds after the second – [0, 10<sup>9</sup> - 1]
+    tm_nsec: i32,
 }
 
 pub fn empty_tm() -> Tm {