Comments
Comments in Rust code follow the general C++ style of line (//) and
block (/* ... */) comment forms. Nested block comments are supported.
Line comments beginning with exactly three slashes (///), and block
comments (/** ... */), are interpreted as a special syntax for doc
attributes. That is, they are equivalent to writing
#[doc="..."] around the body of the comment, i.e., /// Foo turns into
#[doc="Foo"].
Line comments beginning with //! and block comments /*! ... */ are
doc comments that apply to the parent of the comment, rather than the item
that follows. That is, they are equivalent to writing #![doc="..."] around
the body of the comment. //! comments are usually used to document
modules that occupy a source file.
Non-doc comments are interpreted as a form of whitespace.