Create "Filter Run Prefix (Examples)" tiddler (#5144)

Move the `+` vs `:intersection` example into a separate Examples tiddler
which can be expanded on later.

editions/tw5.com/tiddlers/filters/syntax/Filter Expression.tid

@@ -37,6 +37,8 @@ In technical / logical terms:
 |`~run` |`:else[run]` |else |... ELSE run |
 ||`:intersection`|intersection of sets||
 
+For the difference between `+` and `:intersection`, see [[Filter Run Prefix (Examples)]].
+
 The input of a run is normally a list of all the non-[[shadow|ShadowTiddlers]] tiddler titles in the wiki (in no particular order). But the `+` prefix can change this:
 
 |Prefix|Input|h
@@ -56,15 +58,3 @@ In order to remove `$:/baz` in any case, existing or not, simply use the `+` pre
 
 * <$link to="is Operator">`foo bar $:/baz +[!is[system]]`</$link>
 * <$link to="prefix Operator">`foo bar $:/baz +[!prefix[$:/]]`</$link>
-
-There is also a difference between the `:intersection` and `+` prefixes due to varying inputs.
-
-The `+` prefix should be thought of as an "AND" in formal logic, e.g. "give me all titles that satisfy condition A ''and'' condition B". But it's not suitable for all cases; if condition B uses a filter operator that replaces its input, then it will be difficult to use the `+` prefix. For example, if you wanted to find out what tags two tiddlers have in common, you might try to write a filter expression like:
-
-* <$link to="tags Operator">`[[field Operator]tags[]] +[[compare Operator]tags[]]`</$link>
-
-But that won't work, because the second filter run will end up throwing away its input and replacing it with an input consisting of the single title `[[compare Operator]]`. So the result you'd get from that filter expression would be just the tags of the `compare Operator` tiddler.
-
-For cases like this, the `:intersection` prefix is what you need. It takes the filter output so far, //sets it aside// in temporary storage, and starts the next filter run with all tiddler titles as input. Then once the latest filter run has completed, it takes the latest output, compares it to the set-aside output, and produces a new output that contains only titles that appeared in both the set-aside output and the latest output. So to get only the tags that the `field Operator` and `compare Operator` tiddlers have in common, you would write a filter expresison like this:
-
-* <$link to="tags Operator">`[[field Operator]tags[]] :intersection[[compare Operator]tags[]]`</$link>

editions/tw5.com/tiddlers/filters/syntax/Filter Run Prefix (Examples).tid

@@ -0,0 +1,25 @@
+created: 20201117073343969
+modified: 20201117074106350
+tags: [[Filter Syntax]]
+title: Filter Run Prefix (Examples)
+
+!! Difference between `+` and `:intersection`
+
+The `+` prefix should be thought of as an "AND" in formal logic, e.g. "give me all titles that satisfy condition A ''and'' condition B". But it's not suitable for all cases; if condition B uses a filter operator that replaces its input, then it will be difficult to use the `+` prefix. For example, if you wanted to find out what tags two tiddlers have in common, you might try to write a filter expression like:
+
+* <$link to="tags Operator">`[[field Operator]tags[]] +[[compare Operator]tags[]]`</$link>
+
+But that won't work, because the second filter run will end up throwing away its input and replacing it with an input consisting of the single title `[[compare Operator]]`. So the result you'd get from that filter expression would be just the tags of the `compare Operator` tiddler.
+
+For cases like this, the `:intersection` prefix is what you need. It takes the filter output so far, //sets it aside//, and starts the next filter run with all tiddler titles as input. Then once the latest filter run has completed, it takes the latest output, compares it to the set-aside output, and produces a new output that contains only titles that appeared in both the set-aside output and the latest output. So to get only the tags that the `field Operator` and `compare Operator` tiddlers have in common, you would write a filter expression like this:
+
+* <$link to="tags Operator">`[[field Operator]tags[]] :intersection[[compare Operator]tags[]]`</$link>
+
+The following examples use the [[field Operator]] and [[compare Operator]] tiddlers and their respective tags.
+
+<<.operator-example 1 "[[field Operator]tags[]]">>
+<<.operator-example 2 "[[compare Operator]tags[]]">>
+
+<<.operator-example 3 "[[field Operator]tags[]] +[[compare Operator]tags[]]" """The "field Operator" tiddler's tags are lost, so only the "compare Operator" tiddler's tags are returned""">>
+
+<<.operator-example 4 "[[field Operator]tags[]] :intersection[[compare Operator]tags[]]" """Returns the tags that both tiddlers have in common""">>