tighten up isMethodContext checks, document it

README.md

@@ -37,6 +37,11 @@ Objects
 Test whether the object is a generic hash `{}` ie `new Object()`, or is an instance of some
 class.  Tests the object constructor.
 
+### qibl.isMethodContext( _this )
+
+Test whether the given `this` is from a global (function call) context or a method call context.
+Method calls have a `this` object that is not `global` and not `qibl`.
+
 ### qibl.copyObject( target, src1, ... )
 
 Assign all enumerable own properties of the sources `src` onto `target`, and return

qibl.js

@@ -86,7 +86,7 @@ function isHash( obj ) {
 }
 
 function isMethodContext( self ) {
-    return self && self !== qibl && self !== global || false;
+    return self && typeof self === 'object' && self !== qibl && self !== global || false;
 }
 
 // transfer the own properties of src onto target, aka Object.assign

test-qibl.js

@@ -50,6 +50,8 @@ module.exports = {
         t.equal(qibl.isMethodContext(qibl), false);
         t.equal(qibl.isMethodContext(global), false);
         t.equal(qibl.isMethodContext({}), true);
+        t.equal(qibl.isMethodContext(123), false);
+        t.equal(qibl.isMethodContext("string"), false);
 
         var isMc = qibl.isMethodContext;
         t.equal(isMc(), false);