Use the terminology "form" for attribute definitions

"Thing" was unsatisfying to me. "Item" was wrong for inner attributes,
since it includes other things.

Author: ehuss

src/attributes.md

@@ -23,10 +23,10 @@ to name, convention, language, and compiler version. Attributes are modeled
 on Attributes in [ECMA-335], with the syntax coming from [ECMA-334] \(C#).
 
 r[attributes.inner]
-_Inner attributes_, written with a bang (`!`) after the hash (`#`), apply to the item that the attribute is declared within.
+_Inner attributes_, written with a bang (`!`) after the hash (`#`), apply to the form that the attribute is declared within.
 
 r[attributes.outer]
-_Outer attributes_, written without the bang after the hash, apply to the thing that follows the attribute.
+_Outer attributes_, written without the bang after the hash, apply to the form that follows the attribute.
 
 r[attributes.input]
 The attribute consists of a path to the attribute, followed by an optional
@@ -57,7 +57,7 @@ Attributes can be classified into the following kinds:
 * [Tool attributes](#tool-attributes)
 
 r[attributes.allowed-position]
-Attributes may be applied to many things in the language:
+Attributes may be applied to many forms in the language:
 
 * All [item declarations] accept outer attributes while [external blocks],
   [functions], [implementations], and [modules] accept inner attributes.
@@ -197,7 +197,7 @@ r[attributes.activity]
 
 r[attributes.activity.intro]
 An attribute is either active or inert. During attribute processing, *active
-attributes* remove themselves from the thing they are on while *inert attributes*
+attributes* remove themselves from the form they are on while *inert attributes*
 stay on.
 
 The [`cfg`] and [`cfg_attr`] attributes are active.