QUIRKS mode.

1. 'alt' attribute is not set (image box should not collapse):
 20px 20px

2. 'alt' attribute is set to a non-empty value (image box should not collapse):
 20px 20px  20px 20px

3. 'alt' attribute is set to empty value (image box should collapse):
0px 0px

4. 'alt' attribute is set to empty value but other attributes/properties prevent collapsing (image box should not collapse):
image box is blockified: 20px 20px
width attribute is set: 20px 20px
height attribute is set: 20px 20px
width and height attributes are set: 20px 20px
inline style with width set: 20px 20px
inline style with height set: 20px 20px
inline style with width and height: 20px 20px