A namespace for nodes in the Sass parse tree.
The Sass parse tree has three states: dynamic, static Sass, and static CSS.
When it‘s first parsed, a Sass document is in the dynamic state. It has nodes for mixin definitions and `@for` loops and so forth, in addition to nodes for CSS rules and properties. Nodes that only appear in this state are called **dynamic nodes**.
{Tree::Node#perform} returns a static Sass tree, which is different. It still has nodes for CSS rules and properties but it doesn‘t have any dynamic-generation-related nodes. The nodes in this state are in the same structure as the Sass document: rules and properties are nested beneath one another. Nodes that can be in this state or in the dynamic state are called **static nodes**.
{Tree::Node#cssize} then returns a static CSS tree. This is like a static Sass tree, but the structure exactly mirrors that of the generated CSS. Rules and properties can‘t be nested beneath one another in this state.
Finally, {Tree::Node#to_s} can be called on a static CSS tree to get the actual CSS code as a string.