Question: What does the Attribute SequenceHold do for you?
Answer: Rule (→) has the SequenceHold Attribute. As a result a rule
such as the one in the next line can be used. If Rule didn't have the
SequenceHold Attribute Rule[y,Sequence[y1,y2,y3]]
would evaluate to Rule[y, y1, y2, y3] which is an invalid expression.
Nine built in commands have the SequenceHold Attribute. They are:
Rule (→), RuleDelayed (:→), Set (=), SetDelayed (:=),
TagSet, TagSetDelayed, Timing, UpSet (:=), UpSetDelayed (^:=)
Created by Mathematica (May 16, 2004)
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