utf8 模块提供对 UTF-8 编码的基本支持。它与 Lua 5.3+ 的 utf8 库兼容。
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utf8.len(s: <string>, i: <number>, j: <number>, lax: <boolean>)
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utf8.char(...)
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utf8.codepoint(s: <string>, i: <number>, j: <number>)
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utf8.codes(s: <string>, lax: <boolean>)
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utf8.offset(s: <string>, n: <number>, i: <number>)
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utf8.sub(s: <string>, i: <number>, j: <number>)
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utf8.reverse(s: <string>)
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utf8.lastof(s: <string>, pattern: <string>, plain: <boolean>)
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utf8.find(s: <string>, pattern: <string>, init: <number>, plain: <boolean>)
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utf8.width(s: <string>)
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utf8.byte(s: <string>, i: <number>, j: <number>)
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