MySQL-style shorthands

UPDATE, MERGE ... SET, and DELETE FROM are pure parser sugar: the parser desugars each into a FOREACH (WHERE guard first, then the writes, and LIMIT 1 becomes a trailing BREAK). The interpreter never sees these forms — it only ever executes the equivalent loop. This is why their semantics are identical to writing the loop by hand.

UPDATE

UPDATE office SET name = "New Office Name" WHERE id = 216000 LIMIT 1;

; is exactly equivalent to:
FOREACH office IN office
    WHERE office.id = 216000
    SET office.name = "New Office Name"
    BREAK;
;

Without WHERE/LIMIT, it updates every element of the group. Assignments take full expressions and multiple comma-separated targets:

UPDATE goods SET cost = cost * 2, level = level + 1 WHERE cost > 500;

UPDATE TAG t SET ... targets a tag instead of a group; UPDATE ROOT SET ... drops the tag filter entirely, targeting every element in the document:

UPDATE TAG ItemSpec SET cost = 0 WHERE cost < 0;
UPDATE ROOT SET reviewed = 1 WHERE cost > 500;

MERGE ... SET

Same shape as UPDATE, but attributes are written only where missing (idempotent) — like MERGE v.attr = ... in loop form:

MERGE arms SET tier = 1;

DELETE FROM

Removes matching elements; the container survives (contrast with DELETE GROUP, which removes the container itself):

DELETE FROM goods WHERE cost > 500;
DELETE FROM ROOT WHERE cost > 500;              ; every element in the document, any tag
DELETE TAG Obsolete;                            ; removes every <Obsolete> element

Full shorthand grammar