Added comments describing the span limit attributes

     * of spans.

     *

     * MARK and POINT are conceptually located <i>between</i> two adjacent characters.

     * A MARK is "attached" to the character on the left hand side, while a POINT

     * tends to stick to the character on the right hand side.

     * A MARK is "attached" to the character before, while a POINT will stick to the character

     * after. The insertion cursor is conceptually located between the MARK and the POINT.

     *

     * As a result, inserting a new character between a MARK and a POINT will leave the MARK

     * unchanged, while the POINT will be shifted, now located after the inserted character and

     * still glued to the same character after it.

     *

     * Depending on whether the insertion happens at the beginning or the end of a span, the span

     * will hence be expanded to <i>include</i> the new character (when the span is using a MARK at

     * its beginning or a POINT at its end) or it will be <i>excluded</i>.

     *

     * Note that <i>before</i> and <i>after</i> here refer to offsets in the String, which are

     * independent from the visual representation of the text (left-to-right or right-to-left).

     */

    public static final int SPAN_POINT_MARK_MASK = 0x33;