22.4.2.4 bstr

This element defines a binary basic string variant type, which can store any valid Unicode character. Unicode characters that cannot be directly represented in XML as defined by the XML 1.0 specification, shall be escaped using the Unicode numerical character representation escape character format xHHHH, where H represents a hexadecimal character in the character’s value. [Example: The Unicode character 8 is not permitted in an XML 1.0 document, so it shall be escaped as x0008. end example] To store the literal form of an escape sequence, the initial underscore shall itself be escaped (i.e. stored as x005F). [Example: The string literal x0008 would be stored as x005F_x0008. end example]

The possible values for this element are defined by the W3C XML Schema string datatype.