The CSS3 Text definition includes a more precise model of where and how letter spacing is applied within elements, one that is distinctly not what is commonly implemented for the letter-spacing property.
Letter-spacing must not be applied at the beginning or at the end of a line. At element boundaries, the total letter spacing between two characters is given by and rendered within the innermost element that contains the boundary.
Default rendering shows letter spacing applied to trailing edge:
Edge test edge
Correct rendering:
Edge test edge
No letter spacing applied at line beginning or end:
Edge test
Correct rendering:
Edge test
Letter spacing at element boundaries is rendered within the common parent:
blahblah
Correct rendering:
blahblah
Letter spacing applied to single character spans has no effect, since letter spacing is determined by the common parent:
blahblah
Correct rendering:
blahblah