Update the documentation to reflect that [..] is now overloaded for…

… sets

Summary: The `[..]` syntax now works for both arrays and sets. Update the documentation to prefer this syntax. Mark the `elements` construct as deprecated.

Differential Revision: D68765862

fbshipit-source-id: 3504dcf737e03c03772dee5a326659ecebbdc3bb

glean/website/docs/angle/guide.md

@@ -496,21 +496,21 @@ If we want to know for a particular file and a particular name, where it is used
 
 ```lang=angle
 XRefsViaNameByFile { file = "foo.py", xrefs = XRefs };
-{ target = { name = "Bar" } } = elements XRefs
+{ target = { name = "Bar" } } = XRefs[..]
 ```
 
-The second line uses the construct `elements` which is similar to the `[..]` syntax for arrays.
+The second line uses the `[..]` syntax which works the same as for arrays, each element of the set `XRefs` is produced as a different result.
 
 We can also create new sets from the results of a query. This is done using the `all` construct. For instance
 `all (1 | 2 | 3)` is a set containing the number `1`, `2`, and `3`.
 
-The `all` construct can be used in combination with the `elements` construct to, for instance, map over a set
+The `all` construct can be used in combination with the `[..]` construct to, for instance, map over a set
 of elements and transform them. In the example below, the second line takes each element of the `StringSet` and
 applies the primitive `prim.toLower` to it. The result is a set where all the strings are lowercase.
 
 ```lang=angle
 StringSet = all ("Foo" | "Bar" | "Baz" );
-all (String = elements StringSet; prim.toLower String)
+all (String = StringSet[..]; prim.toLower String)
 ```
 
 ## String prefix

glean/website/docs/angle/reference.md

@@ -83,7 +83,7 @@ Terms have the following forms:
 
   *term* `[..]`
 
-> All the elements of the array **term**
+> All the elements of **term**, which is either an array or a set.
 
   *term₁* `|` *term₂*
 
@@ -93,7 +93,7 @@ Terms have the following forms:
 
   `elements` *term*
 
-> All the elements of the set **term**
+> **Deprecated**, use the `[..]` syntax above. All the elements of the set **term**
 
   `all` *query*