RepeatingElement
RepeatingElement[spec] represents an arbitrarily repeated type of element in an interpreter, API or form specification.
RepeatingElement[spec,max] represents an element that can appear at most max times.
RepeatingElement[spec,{min,max}] represents an element that can appear between min and max times.
RepeatingElement[spec,{n,{min,max}}] represents an element that initially appears n times in a form.
RepeatingElement[spec,{{i,n},{min,max}}] represents an element where i takes successive values.
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