JSONiq follows the W3C standard for the map operator, except that it changes the syntax for the context item to $$ instead of the . syntax.
The following explanations, provided as an informal summary for convenience, are non-normative.
Figure 60. SimpleMapExpr
Figure 61. ContextItemExpr
JSONiq provides a shortcut for a for-return construct, automatically binding each item in the left-hand-side sequence to the context item.
Example 135. A simple map
(1 to 10) ! ($$ * 2)
Result (run with Zorba): 2 4 6 8 10 12 14 16 18 20
Example 136. An equivalent query
for $i in 1 to 10 return $i * 2
Result (run with Zorba): 2 4 6 8 10 12 14 16 18 20