Update doc comments

yash-semantics/src/command.rs

@@ -34,7 +34,8 @@ use yash_syntax::syntax;
 pub trait Command {
  /// Executes this command.
  ///
- /// TODO Elaborate: The exit status must be updated during execution.
+ /// Implementations of this method is expected to update `env.exit_status`
+ /// reflecting the result of the command execution.
  #[allow(async_fn_in_trait)] // We don't support Send
  async fn execute(&self, env: &mut Env) -> Result;
 }

yash-semantics/src/expansion/initial/text.rs

@@ -61,13 +61,11 @@ use yash_syntax::syntax::Unquote;
 /// as in `"${@}"`, it produces the correct number of fields exactly matching
 /// the current positional parameters. Especially if there are zero positional
 /// parameters, it expands to zero fields.
-/// (TODO: Elaborate on how that works in this function)
 /// - `*` expands to all positional parameters. When expanded in double-quotes
 /// as in `"${*}"`, the result is a concatenation of all the positional
 /// parameters, each separated by the first character of the `IFS` variable
 /// (or by a space if the variable is unset, or by nothing if it is an empty
 /// string). When expanded outside double-quotes, `*` expands the same as `@`.
-/// (TODO: Elaborate on how that works in this function)
 /// - `#` expands to the number of positional parameters.
 /// - `-` expands to a string that is a concatenation of the short names of
 /// options matching the current option states in the environment.