Add comment to useless range check

src/format/parse.rs

@@ -214,7 +214,11 @@ fn parse_rfc3339<'a>(parsed: &mut Parsed, mut s: &'a str) -> ParseResult<(&'a st
     }
 
     let offset = try_consume!(scan::timezone_offset(s, |s| scan::char(s, b':'), true, false, true));
-    if offset <= -86_400 || offset >= 86_400 {
+    // This range check is similar to the one in `FixedOffset::east_opt`, so it would be redundant.
+    // But it is possible to read the offset directly from `Parsed`. We want to only successfully
+    // populate `Parsed` if the input is fully valid RFC 3339.
+    const MAX_OFFSET: i32 = 23 * 3600 + 59 * 60;
+    if offset < -MAX_OFFSET || offset > MAX_OFFSET {
         return Err(OUT_OF_RANGE);
     }
     parsed.set_offset(i64::from(offset))?;