Review and update changes

`file` should be a contextual keyword. Fix some other errors of omission.

Author: BillWagner

standard/classes.md

@@ -82,15 +82,15 @@ When a partial type declaration ([§15.2.7](classes.md#1527-partial-type-declara
 
 The `abstract`, `sealed`, and `static` modifiers are discussed in the following subclauses.
 
-The `file` modifier specifies that the type being declared is local to its parent compilation unit. A compilation unit containing a `file`-modified type shall not also contain a type declaration having the same name but without the `file` modifier.
+The `file` modifier specifies that the type being declared is local to its parent compilation unit. A compilation unit containing a `file`-modified type shall not also contain a type declaration having the same name but without the `file` modifier. (`file` is a contextual keyword (§6.4.4) that has special meaning when used as a top-level type modifier.)
 
 The `file` modifier shall only appear in a type declaration for a top-level type.
 
 When a type declaration contains the `file` modifier, that type is said to be a ***file-local type***.
 
-The implementation shall guarantee that file-local types with the same name declared in different compilation units, are distinct at runtime. The implementation shall guarantee that a file-local type with the same name as a non-file-local type declared in different compilation units, are distinct at runtime.
+The implementation shall guarantee that two type declarations are distinct at runtime when either both are file-local types with the same name declared in different compilation units, or one is a file-local type and the other is a non-file-local type with the same name.
 
-A file-local class that is an attribute type may be used an as attribute within both file-local types and non-file-local types, just as if the attribute type were a non-file-local class.
+A file-local class that is an attribute type may be used as an attribute within both file-local types and non-file-local types, just as if the attribute type were a non-file-local class.
 
 #### 15.2.2.2 Abstract classes
 
@@ -811,6 +811,8 @@ The modifier `partial` is used when defining a class, struct, or interface type
 
 Each part of a ***partial type*** declaration shall include a `partial` modifier and shall be declared in the same namespace or containing type as the other parts. The `partial` modifier indicates that additional parts of the type declaration might exist elsewhere, but the existence of such additional parts is not a requirement; it is valid for the only declaration of a type to include the `partial` modifier. It is valid for only one declaration of a partial type to include the base class or implemented interfaces. However, all declarations of a base class or implemented interfaces shall match, including the nullability of any specified type arguments.
 
+For a partial type, either all parts shall include the `file` modifier and be declared in the same compilation unit, or no part shall include the `file` modifier.
+
 All parts of a partial type shall be compiled together such that the parts can be merged at compile-time. Partial types specifically do not allow already compiled types to be extended.
 
 Nested types may be declared in multiple parts by using the `partial` modifier. Typically, the containing type is declared using `partial` as well, and each part of the nested type is declared in a different part of the containing type.

standard/lexical-structure.md

@@ -588,7 +588,7 @@ keyword
     | 'byte'     | 'case'     | 'catch'      | 'char'      | 'checked'
     | 'class'    | 'const'    | 'continue'   | 'decimal'   | DEFAULT
     | 'delegate' | 'do'       | 'double'     | 'else'      | 'enum'
-    | 'event'    | 'explicit' | 'extern'     | FALSE       | 'file'      | 'finally'
+    | 'event'    | 'explicit' | 'extern'     | FALSE       | 'finally'
     | 'fixed'    | 'float'    | 'for'        | 'foreach'   | 'goto'
     | 'if'       | 'implicit' | 'in'         | 'int'       | 'interface'
     | 'internal' | 'is'       | 'lock'       | 'long'      | 'namespace'
@@ -609,13 +609,13 @@ A ***contextual keyword*** is an identifier-like sequence of characters that has
 contextual_keyword
     : 'add'      | 'alias'      | 'and'        | 'ascending' | 'async'
     | 'await'    | 'by'         | 'Cdecl'      | 'descending'| 'dynamic'
-    | 'equals'   | 'Fastcall'   | 'from'       | 'get'       | 'global'
-    | 'group'    | 'init'       | 'into'       | 'join'      | 'let'
-    | 'managed'  | 'nameof'     | 'nint'       | 'not'       | 'notnull'
-    | 'nuint'    | 'on'         | 'or'         | 'orderby'   | 'partial'
-    | 'record'   | 'remove'     | 'select'     | 'set'       | 'Stdcall'
-    | 'Thiscall' | 'unmanaged'  | 'value'      | 'var'       | 'when'
-    | 'where'    | 'yield'
+    | 'equals'   | 'Fastcall'   | 'file'       | 'from'      | 'get'
+    | 'global'   | 'group'      | 'init'       | 'into'      | 'join'
+    | 'let'      | 'managed'    | 'nameof'     | 'nint'      | 'not'
+    | 'notnull'  | 'nuint'      | 'on'          | 'or'        | 'orderby'
+    | 'partial'  | 'record'     | 'remove'     | 'select'    | 'set'
+    | 'Stdcall'  | 'Thiscall'   | 'unmanaged'  | 'value'     | 'var'
+    | 'when'     | 'where'      | 'yield'
     ;
 ```