CSS-OM is like DOM, but for style sheets
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Access to rules, properties, values, modules, etc. from within a program
 
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Insert rules, change values, remove properties,...
 
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"Smart" functions: you can set a value in cm and query it in inch, etc.
 
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Same functions for property declarations in a style sheet and for property
declarations on an HTML/XML element (STYLE attribute)
 
There are some CSS-specific APIs and some generic ones, on which to build
for other style languages.