Clarifying doc text about cross-thread sharing
//! for allocating and initializing thread-local data. (Technically, this data is stored in the
//! addon's [module instance][environment], which is equivalent to being thread-local.)
//!
-//! A common example is when an addon defines a custom datatype, which cannot be used across
-//! separate threads. The constructor for the datatype can be [rooted](crate::handle::Root) and
+//! A common example is when an addon needs to maintain a reference to a JavaScript value. References cannot
+//! be used across separate threads. The constructor for the datatype can be [rooted](crate::handle::Root) and
//! saved in thread-local storage:
//!
//! ```
