In all other cases where we cannot find the beginning of a tag, we return the empty string.
在无法找到标签开头的其他所有情况下，我们返回一个空字符串。
You might be asking why the \W+ is necessary: \b is the empty string at the beginning or end of a word.
您可能会提出疑问，为什么 \W+是必需的：\b 是位于单词开头或结尾的空字符串。
This is different from using the empty string, which indicates that the property exists but has no value.
这与使用空字符串不同，空字符串表示属性存在但是没有值。
This both says I'm going to accept a parameter called tracegroups, and makes its default value the empty string.
引号中的两个字段表明，我将要接受名为tracegroups 的参数，并且它的缺省值为空字符串。
If the schema is NULL or the empty string, the procedure restores the schema to the name from where it was backed up.
如果模式是NULL或空字符串，那么这个过程采用备份时的模式名进行恢复。
The current design makes it hard to distinguish between an attribute whose value is the empty string and one that isn't present at all.
当前设计很难区分值为空字符串的属性和值根本不存在的属性。
The call to the preg_replace() function replaces the dollar sign, any whitespace, and every comma with the empty string, yielding what's supposed to be an integer.
调用 preg_replace()函数将用空字符串替换美元符号、所有空格和每个逗号，生成认为是整数的内容。
Note that I have to check that the attribute is actually present, since when it's absent the contains test would return true (the empty string is contained in all strings).
我必须检查这个属性实际上是否出现，因为当没有这个属性时，contains测试将返回true(所有字符串都包含空字符串)。
Bundle-Version: a version of the form major.minor.micro.qualifier where the first three elements are numeric (defaulting to 0) and qualifier is textual (defaulting to the empty string).
Bundle - Version： major . minor . micro .qualifier形式的版本号，前三个元素是数字(缺省是0)，qualifier则是文本(缺省是空字符串)。
Bundle-Version: a version of the form major.minor.micro.qualifier where the first three elements are numeric (defaulting to 0) and qualifier is textual (defaulting to the empty string).
Bundle - Version： major . minor . micro .qualifier形式的版本号，前三个元素是数字(缺省是0)，qualifier则是文本(缺省是空字符串)。
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