Specifies the spacing between letters to use for the text. Letter spacing is specified as a ratio to the font-size property: a default value of 0 means that the text symbol will use the default letter spacing for the font used.
You can also specify negative values for letter spacing to make the text more compact.
This property applies to both point-based and line-based text.
define font-size : 10 text-line-spacing : 0.25
specifies that the there will be additional 2.5 pixels (approximately) between each letter of the text.