They may appear in any order. Attribute names are always case-insensitive.
Attribute values are generally case-insensitive.
The other options specify vertical alignment of text relative to the image on the same line. It is mainly used to create custom image dimensions without physically changing the image itself. It can also be used to speed up display of the document being downloaded so it can pre-render the document with image placeholders while the images download. Positive integer pixel values. Positive integer pixel values.