FEAT: enabling T as a delimiter between date and time and Z as a zero timezone, so subset of ISO8601 datetime values are loadable from Rebol.

Example:
```
>> 2013-11-08T17:01
== 8-Nov-2013/17:01
>> 2013-11-08T17:01+0100
== 8-Nov-2013/17:01+1:00
>> 2013-11-08T17:01Z
== 8-Nov-2013/17:01
```

Related issues:
metaeducation/rebol-issues#438
metaeducation/rebol-issues#2089
metaeducation/rebol-issues#2092

Author: Oldes

src/core/l-scan.c

@@ -981,7 +981,8 @@
 
 			return -TOKEN_INTEGER;
 		}
-		if (HAS_LEX_FLAG(flags, LEX_SPECIAL_COLON)) return TOKEN_TIME;  /* 12:34 */
+		if (HAS_LEX_FLAG(flags, LEX_SPECIAL_COLON))
+			return (HAS_LEX_FLAG(flags, LEX_SPECIAL_WORD) ? TOKEN_DATE : TOKEN_TIME);  /* iso8601 datetime or 12:34 */
 		if (HAS_LEX_FLAG(flags, LEX_SPECIAL_PERIOD)) {  /* 1.2 1.2.3 1,200.3 1.200,3 1.E-2 */
 			if (Skip_To_Char(cp, scan_state->end, 'x')) return TOKEN_PAIR;
 			cp = Skip_To_Char(cp, scan_state->end, '.');

src/core/l-types.c

@@ -525,7 +525,7 @@ bad_hex:	Trap0(RE_INVALID_CHARS);
 	VAL_TIME(value) = NO_TIME;
 	if (cp >= end) goto end_date;
 
-	if (*cp == '/' || *cp == ' ') {
+	if (*cp == '/' || *cp == 'T' || *cp == ' ') { //@@ Oldes: is the check for space really needed here?
 		sep = *cp++;
 		if (cp >= end) goto end_date;
 		cp = Scan_Time(cp, 0, value);
@@ -535,12 +535,19 @@ bad_hex:	Trap0(RE_INVALID_CHARS);
 
 	if (*cp == sep) cp++;
 
+	if (*cp == 'Z') {
+		// 'Z' must be last char in the ISO8601 date (if used).
+		if (++cp == end) goto end_date; // valid timezone 0:0
+		else return 0;
+	}
 	// Time zone can be 12:30 or 1230 (optional hour indicator)
 	if (*cp == '-' || *cp == '+') {
 		if (cp >= end) goto end_date;
 		ep = Grab_Int(cp+1, &num);
 		if (ep-cp == 0) return 0;
 		if (*ep != ':') {
+			// An integer is assumed to be HHMM format
+			// https://github.com/rebol/rebol-issues/issues/1411#issuecomment-170907151
 			int h, m;
 			if (num < -1500 || num > 1500) return 0;
 			h = (num / 100);

src/tests/run-tests.r3

@@ -28,6 +28,7 @@ dt [ ;- delta time
 	wrap load %units/codecs-test.r3
 	wrap load %units/series-test.r3
 	wrap load %units/compress-test.r3
+	wrap load %units/date-test.r3
 
 	recycle/torture
 	recycle

src/tests/units/date-test.r3

@@ -0,0 +1,37 @@
+Rebol [
+	Title:   "Rebol3 date test script"
+	Author:  "Oldes, Peter W A Wood"
+	File: 	 %date-test.r3
+	Tabs:	 4
+	Needs:   [%../quick-test-module.r3]
+]
+
+~~~start-file~~~ "date"
+
+===start-group=== "ISO88601 subset"
+	--test-- "ISO88601 basic load"
+		--assert 8-Nov-2013/17:01 = load "2013-11-08T17:01"
+		--assert 8-Nov-2013/17:01 = load "2013-11-08T17:01Z"
+		--assert 8-Nov-2013/17:01+1:00 = load "2013-11-08T17:01+0100"
+		--assert 8-Nov-2013/17:01-1:00 = load "2013-11-08T17:01-0100"
+		--assert 8-Nov-2013/17:01+1:00 = load "2013-11-08T17:01+01:00"
+	--test-- "basic load of not fully standard ISO88601"
+		--assert 8-Nov-2013/17:01 = load "2013/11/08T17:01"
+		--assert 8-Nov-2013/17:01 = load "2013/11/08T17:01Z"
+		--assert 8-Nov-2013/17:01+1:00 = load "2013/11/08T17:01+0100"
+		--assert 8-Nov-2013/17:01+1:00 = load "2013/11/08T17:01+01:00"
+	--test-- "Invalid ISO88601 dates"
+		--assert error? try [load "2013-11-08T17:01Z0100"]
+		--assert error? try [load "2013/11/08T17:01Z0100"]
+
+	--test-- "Using ISO88601 datetime in a path"
+		;@@ https://github.com/rebol/rebol-issues/issues/2089
+		b: [8-Nov-2013/17:01 "foo"]
+		--assert "foo" = b/2013-11-08T17:01
+
+===end-group===
+
+
+===end-group===
+	
+~~~end-file~~~