Boolean or logical variables can be contained in one word . 布尔量或逻辑变量可占用一个字。
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An operation is permitted on a result tree fragment only if that operation would be permitted on a string the operation on the string may involve first converting the string to a number or boolean 仅当一个操作也能运用于字符串操作时，它才能被用于结果树片段对串操作的操作可能涉及先将串转化为数字或布尔量。
