code: private boolean isBlockCommented(int startLine, int endLine, String[] prefixes, IDocument document) {
  
  		try {
  
  			// check for occurrences of prefixes in the given lines
  			for (int i= startLine; i <= endLine; i++) {
  
  				IRegion line= document.getLineInformation(i);
  				String text= document.get(line.getOffset(), line.getLength());
  
  				int[] found= TextUtilities.indexOf(prefixes, text, 0);
  
  				if (found[0] == -1)
  					// found a line which is not commented
  					return false;
  
  				String s= document.get(line.getOffset(), found[0]);
  				s= s.trim();
  				if (s.length() != 0)
  					// found a line which is not commented
  					return false;
  
  			}
  
  			return true;
  
  		} catch (BadLocationException x) {
  			// should not happen
  			VdmUIPlugin.log(x);
  		}
  
  		return false;
  	}
docs: Determines whether each line is prefixed by one of the prefixes.
  
  @param startLine Start line in document
  @param endLine End line in document
  @param prefixes Possible comment prefixes
  @param document The document
  @return <code>true</code> iff each line from <code>startLine</code>
  to and including <code>endLine</code> is prepended by one
  of the <code>prefixes</code>, ignoring whitespace at the
  begin of line