Normalize whitespace in implicitly or explicitly selected element having attribute
space="preserve", typically a program listing.
Normalizing whitespace means:
replacing tab characters by a number of space characters;
removing the space characters which are common to the beginning of all text lines, that is, removing the superfluous “indentation” in the program listing;
removing the (useless) space characters found just before newline characters.
tab_width represents the maximum number of space characters for an expanded tab character. If this parameter is not specified, a dialog box is displayed to let the user specify
tab_width, an integer between 1 and 16, typically 4 or 8.
normalizeWhiteSpacePre normalizeWhiteSpacePre 4