The length unit indicates an addition to the default space between characters. Values can be negative, but there may be implementation-specific limits. The UA is free to select the exact spacing algorithm. The letter spacing may also be influenced by justification (which is a value of the 'align' property).

      BLOCKQUOTE { letter-spacing: 0.1em }
      

Here, the letter-spacing between each character in 'BLOCKQUOTE' elements would be increased by '0.1em'.

With a value of 'normal', the UAs may change the space between letters to justify text. This will not happen if 'letter-spacing' is explicitly set to a <length> value:

      BLOCKQUOTE { letter-spacing: 0 }
      BLOCKQUOTE { letter-spacing: 0cm }
      

When the resultant space between two letters is not the same as the default space, UAs should not use ligatures.

CSS1 core: UAs may interpret any value of 'letter-spacing' as 'normal'.