Using 'metavalues' for "metamethods" that are not methods

Several "metamethods" are not required to be methods (functions),
so it seems clearer not to call them metamethods. The manual now
uses the word 'metavalue' for those values.

manual/manual.of

@@ -306,11 +306,14 @@ Lua calls this function to perform the addition.
 
 The key for each event in a metatable is a string
 with the event name prefixed by two underscores;
-the corresponding values are called @def{metamethods}.
+the corresponding value is called a @def{metavalue}.
+For most events, the metavalue must be a function,
+which is then called a @def{metamethod}.
 In the previous example, the key is the string @St{__add}
 and the metamethod is the function that performs the addition.
 Unless stated otherwise,
-metamethods should be function values.
+a metamethod may in fact be any @x{callable value},
+which is either a function or a value with a @id{__call} metamethod.
 
 You can query the metatable of any value
 using the @Lid{getmetatable} function.
@@ -468,19 +471,19 @@ Behavior similar to the less than operation.
 The indexing access operation @T{table[key]}.
 This event happens when @id{table} is not a table or
 when @id{key} is not present in @id{table}.
-The metamethod is looked up in the metatable of @id{table}.
+The metavalue is looked up in the metatable of @id{table}.
 
-Despite the name,
-the metamethod for this event can be either a function or a table.
+The metavalue for this event can be either a function, a table,
+or any value with an @id{__index} metavalue.
 If it is a function,
 it is called with @id{table} and @id{key} as arguments,
 and the result of the call
 (adjusted to one value)
 is the result of the operation.
-If it is a table,
-the final result is the result of indexing this table with @id{key}.
+Otherwise,
+the final result is the result of indexing this metavalue with @id{key}.
 This indexing is regular, not raw,
-and therefore can trigger another metamethod.
+and therefore can trigger another @id{__index} metavalue.
 }
 
 @item{@idx{__newindex}|
@@ -488,18 +491,20 @@ The indexing assignment @T{table[key] = value}.
 Like the index event,
 this event happens when @id{table} is not a table or
 when @id{key} is not present in @id{table}.
-The metamethod is looked up in @id{table}.
+The metavalue is looked up in the metatable of @id{table}.
 
 Like with indexing,
-the metamethod for this event can be either a function or a table.
+the metavalue for this event can be either a function, a table,
+or any value with an @id{__newindex} metavalue.
 If it is a function,
 it is called with @id{table}, @id{key}, and @id{value} as arguments.
-If it is a table,
-Lua does an indexing assignment to this table with the same key and value.
+Otherwise,
+Lua repeats the indexing assignment over this metavalue
+with the same key and value.
 This assignment is regular, not raw,
-and therefore can trigger another metamethod.
+and therefore can trigger another @id{__newindex} metavalue.
 
-Whenever there is a @idx{__newindex} metamethod,
+Whenever a @idx{__newindex} metavalue is invoked,
 Lua does not perform the primitive assignment.
 If needed,
 the metamethod itself can call @Lid{rawset}
@@ -760,7 +765,7 @@ In any case, if either the key or the value is collected,
 the whole pair is removed from the table.
 The weakness of a table is controlled by the
 @idx{__mode} field of its metatable.
-This field, if present, must be one of the following strings:
+This metavalue, if present, must be one of the following strings:
 @St{k}, for a table with weak keys;
 @St{v}, for a table with weak values;
 or @St{kv}, for a table with both weak keys and values.
@@ -3836,7 +3841,7 @@ Similar to @Lid{lua_gettable}, but does a raw access
 Pushes onto the stack the value @T{t[n]},
 where @id{t} is the table at the given index.
 The access is raw,
-that is, it does not invoke the @idx{__index} metamethod.
+that is, it does not use the @idx{__index} metavalue.
 
 Returns the type of the pushed value.
 
@@ -3849,7 +3854,7 @@ Pushes onto the stack the value @T{t[k]},
 where @id{t} is the table at the given index and
 @id{k} is the pointer @id{p} represented as a light userdata.
 The access is raw;
-that is, it does not invoke the @idx{__index} metamethod.
+that is, it does not use the @idx{__index} metavalue.
 
 Returns the type of the pushed value.
 
@@ -3885,7 +3890,7 @@ and @id{v} is the value on the top of the stack.
 
 This function pops the value from the stack.
 The assignment is raw,
-that is, it does not invoke the @idx{__newindex} metamethod.
+that is, it does not use the @idx{__newindex} metavalue.
 
 }
 
@@ -3899,7 +3904,7 @@ and @id{v} is the value on the top of the stack.
 
 This function pops the value from the stack.
 The assignment is raw,
-that is, it does not invoke @idx{__newindex} metamethod.
+that is, it does not use the @idx{__newindex} metavalue.
 
 }
 
@@ -6275,7 +6280,7 @@ Returns a boolean.
 
 @LibEntry{rawget (table, index)|
 Gets the real value of @T{table[index]},
-without invoking the @idx{__index} metamethod.
+without using the @idx{__index} metavalue.
 @id{table} must be a table;
 @id{index} may be any value.
 
@@ -6291,7 +6296,7 @@ Returns an integer.
 
 @LibEntry{rawset (table, index, value)|
 Sets the real value of @T{table[index]} to @id{value},
-without invoking the @idx{__newindex} metamethod.
+without using the @idx{__newindex} metavalue.
 @id{table} must be a table,
 @id{index} any value different from @nil and @x{NaN},
 and @id{value} any Lua value.