new batch of docs

docs/content/guide/dev_guide.introduction.ngdoc

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+@workInProgress
+@ngdoc overview
+@name Developer Guide: Introduction
+@description
+
+
+Angular is pure client-side technology, written entirely in JavaScript. It works with the
+long-established technologies of the web (HTML, CSS, and JavaScript) to make the development of web
+apps easier and faster than ever before.
+
+
+One important way that angular simplifies web development is by increasing the level of abstraction
+between the developer and most low-level web app development tasks. Angular automatically takes
+care of many of these tasks, including:
+
+
+* DOM Manipulation
+* Setting Up Listeners and Notifiers
+* Input Validation
+
+
+Because angular handles much of the work involved in these tasks, developers can concentrate more
+on application logic and less on repetitive, error-prone, lower-level coding.
+
+
+At the same time that angular simplifies the development of web apps, it brings relatively
+sophisticated techniques to the client-side, including:
+
+
+* Separation of data, application logic, and presentation components
+* Data Binding between data and presentation components
+* Services (common web app operations, implemented as substitutable objects)
+* Dependency Injection (used primarily for wiring together services)
+* An extensible HTML compiler (written entirely in JavaScript)
+* Ease of Testing
+
+
+These techniques have been for the most part absent from the client-side for far too long.
+
+
+## Single-page / Round-trip Applications
+
+
+You can use angular to develop both single-page and round-trip apps, but angular is designed
+primarily for developing single-page apps. Angular supports browser history, forward and back
+buttons, and bookmarking in single-page apps.
+
+
+You normally wouldn't want to load angular with every page change, as would be the case with using
+angular in a round-trip app. However, it would make sense to do so if you were adding a subset of
+angular's features (for example, templates to leverage angular's data-binding feature) to an
+existing round-trip app. You might follow this course of action if you were migrating an older app
+to a single-page angular app.