Converts the path $urlElement into a new alias url which only conists of valid characters in the URL. For non-Unicode setups this means character in the range a-z, numbers and _, for Unicode setups it means all characters except space, &, ;, /, :, =, ?, [, ], (, ), -

Invalid characters are converted to -.

Returns:: the converted element

Example with a non-Unicode setup

'My car' => 'My-car' 'What is this?' => 'What-is-this' 'This & that' => 'This-that' 'myfile.tpl' => 'Myfile-tpl', 'øæå' => 'oeaeaa'