[doc] Time class document updated.

Author: akr

timev.rb

@@ -47,33 +47,38 @@
 #
 # == \Time Internal Representation
 #
-# Time implementation uses a signed 63 bit integer, Integer, or
-# Rational.
-# It is a number of nanoseconds since the _Epoch_.
+# Conceptually, Time class uses a Rational value to represent the number of
+# nanoseconds from _Epoch_, 1970-01-01 00:00:00 UTC.
+# There are no boundary or resolution limitations.
+# The value can be obtaind using Time#to_r.
+#
+# The Time class always uses the Gregorian calendar.
+# I.e. the proleptic Gregorian calendar is used.
+# Other calendars, such as Julian calendar, are not supported.
+#
+# The implementation uses a signed 63 bit integer or Integer (Bignum) to
+# represent the Rational values if possible.
+# (The signed 63 bit integers are used regardless of 32 and 64 bit environments.)
 # The signed 63 bit integer can represent 1823-11-12 to 2116-02-20.
 # When Integer or Rational is used (before 1823, after 2116, under
 # nanosecond), Time works slower than when the signed 63 bit integer is used.
 #
 # Ruby uses the C function +localtime+ and +gmtime+ to map between the number
 # and 6-tuple (year,month,day,hour,minute,second).
-# +localtime+ is used for local time and "gmtime" is used for UTC.
+# +localtime+ is used for local time and +gmtime+ is used for UTC.
 #
 # Integer and Rational has no range limit, but the localtime and
 # gmtime has range limits due to the C types +time_t+ and <tt>struct tm</tt>.
 # If that limit is exceeded, Ruby extrapolates the localtime function.
 #
-# The Time class always uses the Gregorian calendar.
-# I.e. the proleptic Gregorian calendar is used.
-# Other calendars, such as Julian calendar, are not supported.
-#
 # +time_t+ can represent 1901-12-14 to 2038-01-19 if it is 32 bit signed integer,
 # -292277022657-01-27 to 292277026596-12-05 if it is 64 bit signed integer.
 # However +localtime+ on some platforms doesn't supports negative +time_t+ (before 1970).
 #
 # <tt>struct tm</tt> has _tm_year_ member to represent years.
 # (<tt>tm_year = 0</tt> means the year 1900.)
 # It is defined as +int+ in the C standard.
-# _tm_year_ can represent between -2147481748 to 2147485547 if +int+ is 32 bit.
+# _tm_year_ can represent years between -2147481748 to 2147485547 if +int+ is 32 bit.
 #
 # Ruby supports leap seconds as far as if the C function +localtime+ and
 # +gmtime+ supports it.