One statement you already seen is:
(theme.name "Foo")
This will, as you guess, set theme name. Here, theme is a namespace and name is expression that sets internal theme name. Every public Theme expressions has a theme prefix, like (theme.print) or (theme.style).
You also learned how to assign some value. In common languages (or configuration files), you often would assign variable like this:
var = value
in Theme language it will be like this:
(var value)
But, beware! You can't use this assignment syntax all over .ewt files; it is valid only in (theme.style) block.
...which brings us to (theme.style) syntax... Each (theme.style) must have a style name and block with a list of variables and their values. For example:
(theme.style "demo-style" [ (var1 "value1") (var2 "value2") ])
implements var1 and var2 in "demo-style" style. Each style block begins with [ and ends with ]. Actually it ends with ]) because "theme.style" starts with (. This is very similar to syntax used to assign values.