Parameter syntax:

'previousChar'|'nextChar'|'previousWord'|'nextWord'|
'previousTextNode'|'nextTextNode'|'previousElement'|
'nextElement'|'textNodeBegin'|'textNodeEnd'|
'elementBegin'|'elementEnd'|'documentBegin'|
'documentEnd'|'lineBegin'|'lineEnd'|'previousLine'|
'nextLine'|'wordBegin'|'wordEnd'

Extends text selection to specified location.