 For example, the modifier / takes one operand, a verb to its left, and produces a verb that applies that verb between each item of its argument.That is, +/ is a verb, defined as 'apply + between the items of your argument' Thus, the sentence
produces the effect of

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J has roughly two dozen of these modifiers.All of them can apply to any verb, even a user-written verb, and users may write their own modifiers.