Mark updates needed in the reference

Author: amartini51

TSPL.docc/ReferenceManual/Declarations.md

@@ -1468,8 +1468,16 @@ func <#function name#>(<#parameters#>) throws -> <#return type#> {
 Calls to a throwing function or method must be wrapped in a `try` or `try!` expression
 (that is, in the scope of a `try` or `try!` operator).
 
+<!-- XXX
+Rule for inferring the thrown error type
+Xref to the guide <doc:ErrorHandling#Specifying-a-Concrete-Error-Type>
+-->
+
 The `throws` keyword is part of a function's type,
 and nonthrowing functions are subtypes of throwing functions.
+<!-- XXX
+Subtyping rule for throws(any Error) vs throws(MyErrorType)
+-->
 As a result, you can use a nonthrowing function
 in a context where a throwing one is expected.
 

TSPL.docc/ReferenceManual/Expressions.md

@@ -924,6 +924,10 @@ explicitly marks a closure as throwing or asynchronous.
 
 If the body of a closure includes a try expression,
 the closure is understood to be throwing.
+<!-- XXX
+The same rule to infer the thrown error type
+applies to closures as to functions.
+-->
 Likewise, if it includes an await expression,
 it's understood to be asynchronous.
 

TSPL.docc/ReferenceManual/Statements.md

@@ -897,7 +897,7 @@ or the boxed protocol type `any Error`.
 If the `do` statement doesn't specify the type of error it throws,
 that type is implied to be `any Error`.
 For more information about working with errors that have explicit types,
-see <!-- XXX xref guide -->.
+see <doc:ErrorHandling#Specifying-a-Concrete-Error-Type>.
 
 If any statement in the `do` code block throws an error,
 program control is transferred

TSPL.docc/ReferenceManual/Types.md

@@ -350,6 +350,14 @@ Function types for functions
 that can throw or rethrow an error must be marked with the `throws` keyword.
 The `throws` keyword is part of a function's type,
 and nonthrowing functions are subtypes of throwing functions.
+<!-- XXX
+A function that throws a concrete error
+is a subtype of one that throws 'any Error'.
+
+TR:
+If EE is a subtype of E,
+is a function that throws EE a subtype of one that throws E?
+-->
 As a result, you can use a nonthrowing function in the same places as a throwing one.
 Throwing and rethrowing functions are described in
 <doc:Declarations#Throwing-Functions-and-Methods>