src/main/java/org/fit/layout/cssbox/BoxNode.java
public boolean containsVisibleTextString()
    {
        String s = getText();
        for (int i = 0; i < s.length(); i++)
        {
            char ch = s.charAt(i);
            if (!Character.isSpaceChar(ch))
                return true;
        }
        return false;
    }
public boolean containsVisibleTextString()
    {
        String s = getText();
        for (int i = 0; i < s.length(); i++)
        {
            char ch = s.charAt(i);
            if (!Character.isSpaceChar(ch))
                return true;
        }
        return false;
    }
Checks if the box text is visible (it does not contain spaces only). This is not equivalent to isWhitespace() because
non-beraking spaces are not whitespace characters but they are not visible.
@return <true> if the box text consists of space characters only