技术上，空字符串作为URI是有效的，但不允许作为名称空间uri。

Null strings are technically valid as URIs, but disallowed as namespace URIs.

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标题(title)，简短的、人类可读的记录主体行；允许使用空字符串(用空的标题元素表示，如)。

A title, which expresses a short, human readable subject line for the entry, and can be a blank string (represented by an empty title element, such as).

youdao

在2002年4月，W3C的XML工作组宣布它正在考虑修订XML名称空间，可能会允许把名称空间前缀指定为空字符串。

In April of 2002, the XML Working Group of the W3C announced it was considering a revision of XML namespaces that would permit the assignment of a namespace prefix to the null string.

youdao

在2002年4月，W3C的XML工作组宣布它正在考虑修订XML名称空间，可能会允许把名称空间前缀指定为空字符串。

In April of 2002, the XML Working Group of the W3C announced it was considering a revision of XML namespaces that would permit the assignment of a namespace prefix to the null string.

youdao