You can use regular expressions to limit which characters are allowed and to be more specific (for example, you can often limit even further what the first character can be).

您可以使用正则表达式来更为详细地限制所允许的字符串(例如，您可以进一步指定第一个字符可以是哪些字母)。

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It's easy to make eating ice cream a regular habit in the summer, but try to limit frozen treats like ice cream to no more than once a week.

在夏天，吃冰淇淋很容易成为一种习惯，但是要努力限制冰的宴飨比如冰淇淋一周不能超过1次。

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Internet auctions function in much the same way as regular auctions, though with a longer time limit.

网络上的拍卖运作方式大体与一般的拍卖无异，但有更长的拍卖期限。

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Ratcheting up the time limit on a regular basis becomes a reasonable way of approximating that perpetuity.

ECONOMIST: Why the rules on copyright need to return to their roots

However, in recent years development has helped limit this and boost far more regular trading.

BBC: Bangladesh bids to boost trade with Burma

This resolution could limit military action to just Iraq, require regular reports to be made to Congress on the progress of the campaign and encourage diplomacy through the UN.

ECONOMIST: We will prevail | The