Change to natural counting in range[N] operator (#3609)

* Add range operator and documentation

* Use 1-based counting in range[N], update docs

core/modules/filters/range.js

@@ -34,8 +34,16 @@ exports.range = function(source,operator,options) {
 	}
 	switch(parts.length) {
 		case 1:
-			beg = 0;
 			end = parts[0];
+			if (end >= 1) {
+				beg = 1;
+			}
+			else if (end <= -1) {
+				beg = -1;
+			}
+			else {
+				return [];
+			}
 			inc = 1;
 			break;
 		case 2:

editions/tw5.com/tiddlers/filters/range.tid

@@ -18,28 +18,31 @@ op-output: a series of evenly spaced numbers ranging from `<begin>` to `<end>`
 <$list variable=n filter="[range[$range$]]"><<n>> </$list>
 \end
 
-The `range` operator allows a range of numbers to be enumerated, similar to a `for` loop in other programming languages.  It's useful in combination with the [[Formula Plugin]].
+The `range` operator produces a list of numbers counting up or down.  It's useful for counting and numbering, or in combination with the [[Formula Plugin]].
 
 |!Purpose|produce a range of numbers|
 |!Input|ignored.|
 |!Parameter|1-3 numbers separated by `,` or `;`.|
-|!Output|A range of numbers starting with |
+|!Output|A series of evenly spaced numbers ranging from `<begin>` to `<end>`|
 |!`!` Output|As ''Output'', but with order reversed.|
 
 The parameter has three forms:
 
-* `<end>`
-* `<begin>,<end>`
-* `<begin>,<end>,<step>`
+|Parameter|Output|h
+|`<end>`|Whole numbers up to `<end>`.|
+|`<begin>,<end>`|Numbers from `<begin>` to `<end>`, spaced by whole numbers.|
+|`<begin>,<end>,<step>`|Numbers from `<begin>` to `<end>` spaced out by `<step>`.|
 
 Each part must be a number, and works as follows:
 
-* `<begin>`: start counting at this number.  Defaults to 0.
+* `<begin>`: start counting at this number.
+** Defaults to 1 if `<end>` is at least 1 (or -1 if `<end>` is at most -1).
 * `<end>`: stop counting at this number.
-** It will be included unless it falls between two steps.
+** This number will appear in the list unless it falls between two steps.
 * `<step>`: count up (or down) by this amount.
-** It may be negated so it counts in the right direction.
-** It cannot be zero.
+** Defaults to 1.
+** Cannot be zero.
+** We always count from `<begin>` toward `<end>`, whether `<step>` is positive or negative.
 
 The number of decimal points in the output is fixed, and based on the parameter with the //most// decimal points.