Read XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition Online
Authors: Michael Kay
\I
(multicharacter escape)
XML 1.0 /XML 1.1
\i
(multicharacter escape)
XML 1.0 /XML 1.1
\S
(multicharacter escape)
\s
(multicharacter escape)
matching with whitespace
\W
(multicharacter escape)
\w
(multicharacter escape)
\P{prop}
(complementary escape)
\p{prop}
(category escape)