diff --git a/README.md b/README.md
index d9788b7..8c1e630 100644
--- a/README.md
+++ b/README.md
@@ -18,16 +18,26 @@ For the command line interface install [mkdoc][] globally (`npm i -g mkdoc`).
 
 ## API
 
-### task
+### mk
 
 ```javascript
-task()
+mk()
 ```
 
 Creates a task collection.
 
 Returns a Task.
 
+### #task
+
+```javascript
+static task()
+```
+
+Adds a task to the default task collection.
+
+Returns a Task.
+
 ### Task
 
 ```javascript
@@ -47,14 +57,37 @@ Adds task function(s) to the list of known tasks.
 ### .run
 
 ```javascript
-Task.prototype.run([opts])
+Task.prototype.run()
 ```
 
 Gets a task runner for this collection of tasks.
 
 Returns a task Runner.
 
-* `opts` processing options.
+### #src
+
+```javascript
+static src()
+```
+
+Parses a markdown string into a stream.
+
+Returns the output stream.
+
+### #dest
+
+```javascript
+static dest([file])
+```
+
+Get a destination output stream.
+
+If the file option is not given a destination stream that prints to
+stdout is returned.
+
+Returns an output stream.
+
+* `file` String path to the output file.
 
 ### runner
 
@@ -80,8 +113,7 @@ Execute task functions.
 
 #### Options
 
-* `list` Array of tasks.
-* `scope` Object task execution scope.
+* `task` Object collection of tasks.
 
 ### .get
 
@@ -95,6 +127,29 @@ Returns a task or undefined.
 
 * `id` Function|String task identifier.
 
+### .series
+
+```javascript
+Runner.prototype.series(list, cb)
+```
+
+Execute task functions in series.
+
+* `list` Array of task functions.
+* `cb` Function callback function.
+
+### .parallel
+
+```javascript
+Runner.prototype.parallel(list[, concurrent], cb)
+```
+
+Execute task functions in parallel.
+
+* `list` Array of task functions.
+* `concurrent` Number number of concurrent calls.
+* `cb` Function callback function.
+
 ### .exec
 
 ```javascript
@@ -103,11 +158,24 @@ Runner.prototype.exec(id, cb)
 
 Execute a task by name identifier.
 
+Dependencies are run in parallel before task execution.
+
 Returns a task or undefined.
 
 * `id` Function|String task identifier.
 * `cb` Function callback function.
 
+### .each
+
+```javascript
+Runner.prototype.each([names], cb)
+```
+
+Execute a list of tasks to by string identifiers.
+
+* `names` Array list of task names.
+* `cb` Function callback function.
+
 ## License
 
 MIT
diff --git a/index.js b/index.js
index 85535c5..032957f 100644
--- a/index.js
+++ b/index.js
@@ -79,7 +79,7 @@ function add() {
   }
 
   if(!args.length) {
-    throw new TypeError('task function(s) expected'); 
+    throw new TypeError('not enough arguments for task()'); 
   }
 
   function gather(args) {
@@ -126,10 +126,13 @@ Task.prototype.run = run;
 mk.src = ast.src;
 
 /**
- *  Get a file write output stream.
+ *  Get a destination output stream.
+ *
+ *  If the file option is not given a destination stream that prints to 
+ *  stdout is returned.
  *
  *  @static {function} dest
- *  @param {String} file path to the output file.
+ *  @param {String} [file] path to the output file.
  *  
  *  @returns an output stream.
  */
diff --git a/runner.js b/runner.js
index ee0fdaa..088aa17 100644
--- a/runner.js
+++ b/runner.js
@@ -114,10 +114,12 @@ function parallel(list, concurrent, cb) {
   concurrent = concurrent || items.length;
 
   function run() {
+    if(complete) {
+      items = items.slice(concurrent);
+    }
     for(var i = 0;i < concurrent;i++) {
       items[i].call(scope, next);
     }
-    items = items.slice(concurrent);
   }
 
   function next(err) {
diff --git a/test/spec/defaults.js b/test/spec/defaults.js
new file mode 100644
index 0000000..9c83141
--- /dev/null
+++ b/test/spec/defaults.js
@@ -0,0 +1,13 @@
+var expect = require('chai').expect
+  , mktask = require('../../index');
+
+describe('mktask:', function() {
+
+  it('should get default task collection', function(done) {
+    // static task() method
+    var res = mktask.task();
+    expect(res).to.be.an('object');
+    done();
+  });
+  
+});
diff --git a/test/spec/dest.js b/test/spec/dest.js
new file mode 100644
index 0000000..6480d4f
--- /dev/null
+++ b/test/spec/dest.js
@@ -0,0 +1,18 @@
+var expect = require('chai').expect
+  , mktask = require('../../index');
+
+describe('mktask:', function() {
+
+  it('should get file write destination stream', function(done) {
+    var res = mktask.dest('target/foo.txt');
+    expect(res).to.be.an('object');
+    done();
+  });
+  
+  it('should get default destination stream', function(done) {
+    var res = mktask.dest();
+    expect(res).to.be.an('object');
+    done();
+  });
+  
+});
diff --git a/test/spec/each.js b/test/spec/each.js
new file mode 100644
index 0000000..d95ab87
--- /dev/null
+++ b/test/spec/each.js
@@ -0,0 +1,48 @@
+var expect = require('chai').expect
+  , mktask = require('../../index');
+
+describe('mktask:', function() {
+
+  it('should iterate task function (each)', function(done) {
+    var mk = mktask()
+      , called = 0;
+    
+    function readme(cb) {
+      called++;
+      cb();
+    }
+      
+    mk.task(readme);
+
+    var runner = mk.run();
+    runner.each([readme.name], function() {
+      expect(called).to.eql(1);
+      done();
+    });
+  });
+
+  it('should iterate all task functions (each)', function(done) {
+    var mk = mktask()
+      , called = 0;
+
+    function api(cb) {
+      called++;
+      cb();
+    }
+    
+    function readme(cb) {
+      called++;
+      cb();
+    }
+      
+    mk.task(api);
+    mk.task(readme);
+
+    var runner = mk.run();
+    runner.each(function() {
+      expect(called).to.eql(2);
+      done();
+    });
+  });
+
+});
diff --git a/test/spec/run.js b/test/spec/exec.js
similarity index 61%
rename from test/spec/run.js
rename to test/spec/exec.js
index 1a9370c..b8b3ce6 100644
--- a/test/spec/run.js
+++ b/test/spec/exec.js
@@ -3,23 +3,6 @@ var expect = require('chai').expect
 
 describe('mktask:', function() {
 
-  it('should get task from runner', function(done) {
-    var mk = mktask()
-      , readme = function readme(){}
-      , res = mk.task(readme)
-      , runner = mk.run();
-
-    expect(res).to.be.an('object');
-    expect(runner).to.be.an('object');
-
-    expect(runner.get(readme)).to.eql(res);
-    expect(runner.get(readme.name)).to.eql(res);
-
-    expect(runner.get('foo')).to.eql(undefined);
-
-    done();
-  });
-
   it('should return task from runner (exec)', function(done) {
     var mk = mktask()
       , readme = function readme(){}
@@ -87,43 +70,6 @@ describe('mktask:', function() {
     });
   });
 
-  it('should exec task functions dependencies in parallel', function(done) {
-    var mk = mktask()
-      , called = 0
-      , docsCalled
-      , apiCalled
-      , readmeCalled;
-
-    function docs(cb) {
-      called++;
-      docsCalled = 1;
-      cb();
-    }
-
-    function api(cb) {
-      called++;
-      apiCalled = 1;
-      cb();
-    }
-    
-    function readme(cb) {
-      called++;
-      readmeCalled = 1;
-      cb();
-    }
-      
-    mk.task([docs, api], readme);
-
-    var runner = mk.run();
-    runner.exec(readme, function() {
-      expect(called).to.eql(3); 
-      expect(docsCalled).to.eql(1); 
-      expect(apiCalled).to.eql(1); 
-      expect(readmeCalled).to.eql(1); 
-      done();
-    });
-  });
-
   it('should callback with error on task function exec', function(done) {
     var mk = mktask()
     
diff --git a/test/spec/parallel.js b/test/spec/parallel.js
new file mode 100644
index 0000000..d707147
--- /dev/null
+++ b/test/spec/parallel.js
@@ -0,0 +1,84 @@
+var expect = require('chai').expect
+  , mktask = require('../../index');
+
+describe('mktask:', function() {
+
+  //it('should exec task functions dependencies in parallel',
+    //function(done) {
+      //var mk = mktask()
+        //, called = 0
+        //, docsCalled
+        //, apiCalled
+        //, readmeCalled;
+
+      //function docs(cb) {
+        //called++;
+        //docsCalled = 1;
+        //cb();
+      //}
+
+      //function api(cb) {
+        //called++;
+        //apiCalled = 1;
+        //cb();
+      //}
+      
+      //function readme(cb) {
+        //called++;
+        //readmeCalled = 1;
+        //cb();
+      //}
+        
+      //mk.task([docs, api], readme);
+
+      //var runner = mk.run();
+      //runner.exec(readme, function() {
+        //expect(called).to.eql(3); 
+        //expect(docsCalled).to.eql(1); 
+        //expect(apiCalled).to.eql(1); 
+        //expect(readmeCalled).to.eql(1); 
+        //done();
+      //});
+    //}
+  //);
+
+  it('should exec task functions dependencies in parallel w/ concurrent',
+    function(done) {
+      var mk = mktask()
+        , called = 0
+        , docsCalled
+        , apiCalled
+        , readmeCalled;
+
+      function docs(cb) {
+        called++;
+        docsCalled = 1;
+        cb();
+      }
+
+      function api(cb) {
+        called++;
+        apiCalled = 1;
+        cb();
+      }
+      
+      function readme(cb) {
+        called++;
+        readmeCalled = 1;
+        cb();
+      }
+        
+      mk.task([docs, api], readme);
+
+      var runner = mk.run();
+      runner.parallel([docs, api, readme], 1, function() {
+        expect(called).to.eql(3); 
+        expect(docsCalled).to.eql(1); 
+        expect(apiCalled).to.eql(1); 
+        expect(readmeCalled).to.eql(1); 
+        done();
+      });
+    }
+  );
+
+});
diff --git a/test/spec/runner.js b/test/spec/runner.js
new file mode 100644
index 0000000..4a32352
--- /dev/null
+++ b/test/spec/runner.js
@@ -0,0 +1,23 @@
+var expect = require('chai').expect
+  , mktask = require('../../index');
+
+describe('mktask:', function() {
+
+  it('should get task from runner', function(done) {
+    var mk = mktask()
+      , readme = function readme(){}
+      , res = mk.task(readme)
+      , runner = mk.run();
+
+    expect(res).to.be.an('object');
+    expect(runner).to.be.an('object');
+
+    expect(runner.get(readme)).to.eql(res);
+    expect(runner.get(readme.name)).to.eql(res);
+
+    expect(runner.get('foo')).to.eql(undefined);
+
+    done();
+  });
+
+});
diff --git a/test/spec/task.js b/test/spec/task.js
index 27b04a6..f0e0451 100644
--- a/test/spec/task.js
+++ b/test/spec/task.js
@@ -95,5 +95,4 @@ describe('mktask:', function() {
     done();
   });
   
-  
 });