Define value of an attribute in construction.
The following construct(s) refer to this construct:
An AttributeValue is part of an AttributeList
inside an ElementConstructor. This expression specifies that
attribute values are either delimited by single quotes or by double quotes.
Some string literals as attribute values:
<example quote1="This is Joe's house."
quote2='I bought a 21" monitor today.'
quote3="He's 5'11" tall."/>