Construct a processing instruction by computing an expression.
The following construct(s) refer to this construct:
A CompPIConstructor constructs a processing instruction (PI)
by computing the enclosed Expr, called content
expression. The name of the element is either a NCName or it
is computed from an expression (name expression).
The value resulting from evaluating the name expression undergoes
atomization, and must be a single atomic value of the type
xs:NCName, xs:string, or
xdt:untypedAtomic, otherwise a type error is raised. If necessary,
the value is cast into type xs:NCName. It is then used as the PI
target.
The content expression is evaluated and, after atomization, converted into a sequence of atomic values each of which is cast into a string and concatenated with a space character between each pair of values. If the result of the expression after atomization is an empty sequence, it is replaced by a string of length zero.
This constructs the processing instruction <?audio-output
beep?> :
let $target := "audio-output",
$content := "beep"
return processing-instruction {$target} {$content}