Syntax

The general syntax for a document type declaration is:

]>

In XML, the root element of the document is the first element in the document (e.g. in XHTML, the root element is html, being the first element opened and last closed). The keywords SYSTEM and PUBLIC suggest what kind of DTD it is (one that is on a private system or one that is open to the public). If the “SYSTEM” keyword is chosen, the URI of the DTD may follow; if the PUBLIC keyword is chosen then the declaration must have a FPI (Formal Public Identifier) following it and then the URI of the DTD (the FPI for XHTML 1.1 is “-//W3C//DTD XHTML 1.1//EN”).

The last part, surrounded by literal [square brackets], is called an internal subset which can be used to add/edit entities or add/edit elements. It is always optional (and sometimes even forbidden within simple SGML profiles, notably those for basic HTML parsers that don’t implement a full SGML parser).

Document type declarations are slightly different in SGML, where you may associate the public identifier with the system identifier, as it is in HTML.

Example

The first line of many World Wide Web pages reads as follows:

This Document Type Declaration for XHTML includes by reference a DTD, whose public identifier is -//W3C//DTD XHTML 1.0 Transitional//EN and whose system identifier is http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd. An entity resolver may use either identifier for locating the referenced external entity. The root element is declared to be html.

HTML 4.01 DTDs

HTML 4.01 Strict does not allow presentational markup with the argument that Cascading Style Sheets should be used for that instead. This is how the strict doctype looks:

Transitional DTD allows some older elements and attributes that have been deprecated:

If frames are used, the frameset doctype must be used instead, like this:

XHTML 1.0 DTDs

XHTML’s DTDs are also Strict, Transitional and Frameset.

XHTML Strict DTD is the most strict DTD available: no deprecated tags are supported and the code must be written correctly.

XHTML Transitional DTD is like the XHTML Strict DTD, but deprecated tags are allowed. This is the most popular current DTD.

XHTML Frameset DTD is the only XHTML DTD that supports Frameset. The DTD is below.

XHTML 1.1 DTD

This is the latest DTD that has the stringency of XHTML 1.0 Strict, and it is based upon the module framework and modules defined in Modularization of XHTML.

XHTML Basic DTDs

XHTML Basic 1.0

XHTML Basic 1.1

XHTML Mobile Profile DTDs

XHTML Mobile Profile 1.0

XHTML Mobile Profile 1.1

XHTML Mobile Profile 1.2

HTML5 DTD-less DOCTYPE

HTML5 uses a DOCTYPE declaration which is very short, due to its lack of references to a Document Type Definition in the form of a URL and/or FPI. All it contains is the tag name of the root element of the document, HTML. In the words of the specification draft itself:

In other words, , case-insensitively.

With the exception of the lack of a URI or the FPI string (the FPI string is treated case sensitively by validators), this format (a case-insensitive match of the string !DOCTYPE HTML) is the same as found in the syntax of the SGML based HTML 4.01 DOCTYPE. Both in HTML4 and in HTML5, the formal syntax is defined in upper case letter, even if both lower case and mixes of lower case upper case are also treated as valid.

However, in XHTML5 the DOCTYPE has to be a case-”sensitive” match of the string “” due to the fact that in ”XHTML” syntax, the HTML elements, including the root element referenced inside the HTML5 DOCTYPE, are required to be in lower case. As well, XHTML only accepts the upper case inside the DOCTYPE string. These rules are not defined by the HTML5 specification itself but by XML and the syntax rules for XHTML DTDs. For the XHTML5 syntax, then Document Type Definitions are permitted as well.

Note, however, that the DOCTYPE is optional in XHTML5 – it may simply be omitted. Omitting it is however not fully compatible with text/html parsers, as these parsers will go into Quirks mode whenever the HTML5 doctype is lacking. This however, is only a problem whenever the document is supposed to be consumed by text/html parser as well as by XHTML (application/xhtml+xml) parsers. Given, however, that the HTML5 specification forbids XML-serialized HTML5 (XHTML5) from being served with any MIME type other than application/xhtml+xml, this is unlikely to be a situation encountered in the real-world. Unlike with the previous versions of XHTML, it is impossible to serve an XHTML5 (that is, HTML5 serialized as XML) document as text/html in any conceivable situation; any situation involving XHTML5 will be served as application/xhtml+xml and parsed as XML in a standards-compliant system.

Adapted from the Wikipedia article Document Type Declaration, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Many major browsers are often tolerant of certain types of error, and may display a document successfully even if it is not syntactically correct. Certain other XML documents can also be validated if they refer to an internal or external DTD.

W3C also offers validation tools for web technologies other than HTML/XHTML, such as MathML or CSS.

Adapted from the Wikipedia article W3C Markup Validation Service, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Adapted from the Wikipedia article History of Internet Explorer, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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PAS 78 covers the general principles of building an accessible website, along with a discussion of how disabled people use computers and websites. The heart of the document covers the Web technologies (HTML, CSS, JavaScript), as well as rich media format (such as PDF, Flash, audio and video). The section on testing covers technical testing (page validation) as well as user testing, including testing with disabled people. The last section covers contracting external companies, focusing on choosing a website developer.

The supplementary documentation contains a number of resources including suggested user profiles for building up test cases, success criteria, suggested questions for web design agencies, available accreditation schemes, how to select a content management system and a collection of references including organisations and books about web accessibility.

Adapted from the Wikipedia article PAS 78, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Fahrner Image Replacement (abbreviated FIR) is a Web design technique that uses Cascading Style Sheets to replace text on a Web page with an image containing that text. It is intended to keep the page accessible to users of screen readers, text-only web browsers, or other browsers where support for images or style sheets is either disabled or nonexistent, while allowing the image to differ between styles. FIR is named for Todd Fahrner, one of the persons originally credited with the idea of image replacement.

Adapted from the Wikipedia article Fahrner Image Replacement, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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David Siegel’s 1996 book ”Creating Killer Web Sites” [http://www.killersites.com/killerSites/core.html] was allegedly the first to publish the Spacer GIF technique. According to Siegel, he invented the trick in his living room.

The use of spacer GIFs has declined due to the prevalence of Cascading Style Sheets (CSS) for laying out web pages, which achieves the same effect by changing the margin or padding on a given element. If used properly, CSS reduces unnecessary code in a web page. Blank 1×1 GIFs are still occasionally used to fix a PNG rendering limitation in Microsoft Internet Explorer versions 5.5 – 6.

Spacer GIFs have begun to be used with the recent advent of “CSS Sprites”. Using a CSS Sprite will place several images on a grid, to display an image placed on a grid, the transparent spacer GIF will be stretched to the size of the grid image, and the grid image will be placed behind the spacer GIF.

Adapted from the Wikipedia article Spacer GIF, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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The ”blink” value of the CSS ”text-decoration” property allows authors to suggest that text should blink without using proprietary tags, but the ”CSS 2.1 Specification” states that “conforming user agents may simply not blink the text” in order to comply with the ”User Agent Accessibility Guidelines”.

Example:

.advertisement {

text-decoration: blink;

}

Adapted from the Wikipedia article Blink element, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Amaya is a direct descendant of the ”Grif” WYSIWYG SGML editor created by Vincent Quint and Irène Vatton at INRIA in the early 1980s, and of the HTML editor Symposia, itself based on Grif, both developed and sold by French software company Grif SA.

Originally designed as a structured text editor (predating SGML) and later as an HTML and Cascading Style Sheets (CSS) editor, it was then expanded to include XML capabilities such as XHTML, MathML and Scalable Vector Graphics (SVG).

Amaya displays free and open image formats such as PNG and SVG, as well as a subset of SVG animation.

Adapted from the Wikipedia article Amaya (web browser), under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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If a user revisits a Web page after only a short interval, the page data may not need to be re-obtained from the source Web server. Almost all web browsers cache recently obtained data, usually on the local hard drive. HTTP requests sent by a browser will usually only ask for data that has changed since the last download. If the locally cached data are still current, it will be reused. Caching helps reduce the amount of Web traffic on the Internet. The decision about expiration is made independently for each downloaded file, whether image, stylesheet, JavaScript, HTML, or whatever other content the site may provide. Thus even on sites with highly dynamic content, many of the basic resources only need to be refreshed occasionally. Web site designers find it worthwhile to collate resources such as CSS data and JavaScript into a few site-wide files so that they can be cached efficiently. This helps reduce page download times and lowers demands on the Web server.

There are other components of the Internet that can cache Web content. Corporate and academic firewalls often cache Web resources requested by one user for the benefit of all. (See also Caching proxy server.) Some search engines also store cached content from websites. Apart from the facilities built into Web servers that can determine when files have been updated and so need to be re-sent, designers of dynamically generated Web pages can control the HTTP headers sent back to requesting users, so that transient or sensitive pages are not cached. Internet banking and news sites frequently use this facility. Data requested with an HTTP ‘GET’ is likely to be cached if other conditions are met; data obtained in response to a ‘POST’ is assumed to depend on the data that was POSTed and so is not cached.

Adapted from the Wikipedia article World Wide Web, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Code editor

Visual Studio, like any other IDE, includes a code editor that supports syntax highlighting and code completion using IntelliSense for not only variables, functions and methods but also language constructs like loops and queries. IntelliSense is supported for the included languages, as well as for XML and for Cascading Style Sheets and JavaScript when developing web sites and web applications. Autocomplete suggestions are popped up in a modeless list box, overlaid on top of the code editor. In Visual Studio 2008 onwards, it can be made temporarily semi-transparent to see the code obstructed by it. The code editor is used for all supported languages.

The Visual Studio code editor also supports setting bookmarks in code for quick navigation. Other navigational aids include collapsing code blocks and incremental search, in addition to normal text search and regex search. The code editor also includes a multi-item clipboard and a task list. The code editor supports code snippets, which are saved templates for repetitive code and can be inserted into code and customized for the project being worked on. A management tool for code snippets is built in as well. These tools are surfaced as floating windows which can be set to automatically hide when unused or docked to the side of the screen. The Visual Studio code editor also supports code refactoring including parameter reordering, variable and method renaming, interface extraction and encapsulation of class members inside properties, among others.

Visual Studio features background compilation (also called incremental compilation). As code is being written, Visual Studio compiles it in the background in order to provide feedback about syntax and compilation errors, which are flagged with a red wavy underline. Warnings are marked with a green underline. Background compilation does not generate executable code, since it requires a different compiler than the one used to generate executable code. Background compilation was initially introduced with Microsoft Visual Basic but has now been expanded for all included languages.

Debugger

Visual Studio includes a debugger that works both as a source-level debugger and as a machine-level debugger. It works with both managed code as well as native code and can be used for debugging applications written in any language supported by Visual Studio. In addition, it can also attach to running processes and monitor and debug those processes. If source code for the running process is available, it displays the code as it is being run. If source code is not available, it can show the disassembly. The Visual Studio debugger can also create memory dumps as well as load them later for debugging. Multi-threaded programs are also supported. The debugger can be configured to be launched when an application running outside the Visual Studio environment crashes.

The debugger allows setting breakpoints (which allow execution to be stopped temporarily at a certain position) and watches (which monitor the values of variables as the execution progresses). Breakpoints can be conditional, meaning they get triggered when the condition is met. Code can be stepped over, i.e., run one line (of source code) at a time. It can either ”step into” functions to debug inside it, or ”step over” it, i.e., the execution of the function body isn’t available for manual inspection. The debugger supports ”Edit and Continue”, i.e., it allows code to be edited as it is being debugged (32 bit only; not supported in 64 bit). When debugging, if the mouse pointer hovers over any variable, its current value is displayed in a tooltip (“data tooltips”), where it can also be modified if desired. During coding, the Visual Studio debugger lets certain functions be invoked manually from the Immediate tool window. The parameters to the method are supplied at the Immediate window.

Designer

Visual Studio includes a host of visual designers to aid in the development of applications. These tools include:

;Windows Forms Designer: The Windows Forms designer is used to build GUI applications using Windows Forms. It includes a palette of UI widgets and controls (including buttons, progress bars, labels, layout containers and other controls) that can be dragged and dropped on a form surface. Layout can be controlled by housing the controls inside other containers or locking them to the side of the form. Controls that display data (like textbox, list box, grid view, etc.) can be data-bound to data sources like databases or queries. The UI is linked with code using an event-driven programming model. The designer generates either C# or VB.NET code for the application.

;WPF Designer: The WPF designer, codenamed ”Cider”, was introduced with Visual Studio 2008. Like the Windows Forms designer it supports the drag and drop metaphor. It is used to author user interfaces targeting Windows Presentation Foundation. It supports all WPF functionality including databinding and automatic layout management. It generates XAML code for the UI. The generated XAML file is compatible with Microsoft Expression Design, the designer-oriented product. The XAML code is linked with code using a code-behind model.

;Web designer/development: Visual Studio also includes a web-site editor and designer that allows web pages to be authored by dragging and dropping widgets. It is used for developing ASP.NET applications and supports HTML, CSS and JavaScript. It uses a code-behind model to link with ASP.NET code. From Visual Studio 2008 onwards, the layout engine used by the web designer is shared with Microsoft Expression Web. There is also ASP.NET MVC support for MVC technology as a separate download and Dynamic Data project available from Microsoft

;Class designer: The Class Designer is used to author and edit the classes (including its members and their access) using UML modeling. The Class Designer can generate C# and VB.NET code outlines for the classes and methods. It can also generate class diagrams from hand-written classes.

;Data designer: The data designer can be used to graphically edit database schemas, including typed tables, primary and foreign keys and constraints. It can also be used to design queries from the graphical view.

;Mapping designer: From Visual Studio 2008 onwards, the mapping designer is used by LINQ to SQL to design the mapping between database schemas and the classes that encapsulate the data. The new solution from ORM approach, ADO.NET Entity Framework, replaces and improves the old technology.

Other tools

;Open Tabs Browser: The open tabs browser is used to list all open tabs and to switch between them. It is invoked using CTRL+TAB.

;Properties Editor: The ”Properties Editor” tool is used to edit properties in a GUI pane inside Visual Studio. It lists all available properties (both read-only and those which can be set) for all objects including classes, forms, web pages and other items.

;Object Browser: The ”Object Browser” is a namespace and class library browser for Microsoft .NET. It can be used to browse the namespaces (which are arranged hierarchically) in managed assemblies. The hierarchy may or may not reflect the organization in the file system.

;Solution Explorer: In Visual Studio parlance, a solution is a set of code files and other resources that are used to build an application. The files in a solution are arranged hierarchically, which might or might not reflect the organization in the file system. The ”Solution Explorer” is used to manage and browse the files in a solution.

;Team Explorer: ”Team Explorer” is used to integrate the capabilities of Team Foundation Server, the Revision Control System into the IDE (and the basis for Microsoft’s CodePlex hosting environment for open source projects). In addition to source control it provides the ability to view and manage individual work items (including bugs, tasks and other documents) and to browse TFS statistics. It is included as part of a TFS install and is also available as a download for Visual Studio 2005 and 2008. Team Explorer is also available as a stand-alone environment solely to access TFS services.

;Data Explorer: ”Data Explorer” is used to manage databases on Microsoft SQL Server instances. It allows creation and alteration of database tables (either by issuing T-SQL commands or by using the Data designer). It can also be used to create queries and stored procedures, with the latter in either T-SQL or in managed code via SQL CLR. Debugging and IntelliSense support is available as well.

;Server Explorer: The ”Server Explorer” tool is used to manage database connections on an accessible computer. It is also used to browse running Windows Services, performance counters, Windows Event Log and message queues and use them as datasource.

;Dotfuscator Software Services Community Edition: Visual Studio includes a free ‘light’ version of PreEmptive Solutions’ Dotfuscator product for code obfuscation and application-size reduction. Starting with Visual Studio 2010, this version of Dotfuscator will include Runtime Intelligence capabilities that allow authors to gather end-user usage, performance, and stability information from their applications running in production.

Extensibility

:

Visual Studio allows developers to write extensions for Visual Studio to extend its capabilities. These extensions “plug into” Visual Studio and extend its functionality. Extensions come in the form of ”macros”, ”add-ins”, and ”packages”. Macros represent repeatable tasks and actions that developers can record programmatically for saving, replaying, and distributing. Macros, however, cannot implement new commands or create tool windows. They are written using Visual Basic and are not compiled. Add-Ins provide access to the Visual Studio object model and can interact with the IDE tools. Add-Ins can be used to implement new functionality and can add new tool windows. Add-Ins are plugged in to the IDE via COM and can be created in any COM-compliant languages. Packages are created using the Visual Studio SDK and provide the highest level of extensibility. They can create designers and other tools, as well as integrate other programming languages. The Visual Studio SDK provides unmanaged APIs as well as a managed API to accomplish these tasks. However, the managed API isn’t as comprehensive as the unmanaged one. Extensions are supported in the Standard (and higher) versions of Visual Studio 2005. Express Editions do not support hosting extensions.

Visual Studio 2008 introduced the Visual Studio Shell that allows for development of a customized version of the IDE. The Visual Studio Shell defines a set of VSPackages that provide the functionality required in any IDE. On top of that, other packages can be added to customize the installation. The Isolated mode of the shell creates a new AppId where the packages are installed. These are to be started with a different executable. It is aimed for development of custom development environments, either for a specific language or a specific scenario. The Integrated mode installs the packages into the AppId of the Professional/Standard/Team System editions, so that the tools integrate into these editions. The Visual Studio Shell is available as a free download.

After the release of Visual Studio 2008, Microsoft created the [http://visualstudiogallery.com/ Visual Studio Gallery]. It serves as the central location for posting information about extensions to Visual Studio. Community developers as well as commercial developers can upload information about their extensions to Visual Studio .NET 2002 through Visual Studio 2010. Users of the site can rate and review the extensions to help assess the quality of extensions being posted. RSS feeds to notify users on updates to the site and tagging features are also planned.

Adapted from the Wikipedia article Microsoft Visual Studio, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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