Web specifications supported in Opera 6

Opera HTML support

Opera version 6 supports HTML 4.01 with these exceptions:

Intrinsic event attributes

These attributes are not supported:

• Any event attribute for option
• ondblclick

Form elements

These form elements are not supported: visual feedback for button, label, legend. These form attributes are not supported: accept, accept-charset, for.

Table elements

Opera supports HTML 3.2 style table elements fully (ie. table, caption, tr, th and td). Opera handles tfoot properly (it is always displayed at the bottom at a table), otherwise Opera doesn't support the new HTML 4.01 elements (col, colgroup, thead, tfoot, tbody) and attributes (abbr, axis, char, charoff, frame, headers, rules and scope). Opera doesn't assign styles to the grouping elements (tbody, tfoot and thead).

Other issues

• The a element attributes coords, charset, and hreflang and shape.
• The frameborder attribute is not supported.
• The bidirectional override element bdo and the dir attribute. The lang attribute is not supported (in for instance q).
• The attributes accesskey, tabindex are not supported.
• Opera supports object, but not the attributes align, classid, codebase, codetype and standby. For plug-ins embed is used.
• Opera doesn't support the applet attributes align and archive
• Opera has no particular support for link apart from rel="stylesheet", nor for the meta attribute scheme or the head attribute profile.
• The deprecated hr noshade attribute has no effect, neither does the deprecated attribute compact. CSS should be used for this.
• Opera follows the HTML 4.01 specification for script and noscript. If any script element doesn't execute, all subsequent noscript element are displayed.

CSS support

Opera 6 supports all of CSS1.

Opera 6 supports all of CSS2 with the exception of:

• Opera 6 is a visual browser and does not support Aural CSS
• these properties: clip, cursor, direction, font-size-adjust, font-stretch, marker-offset, marks, text-shadow, unicode-bidi, and all outline properties
• Linux only: the system values on the font property as well as system colors
• the values added to list-style-type in CSS2
• these property/value combination: 'display: marker', 'text-align: <string>', 'visibility: collapse', 'content: <url>', 'overflow: scroll', 'overflow:auto'
• named pages (as described in section 13.3.2)
• the '@font-face' construct

All CSS2 selectors are supported with the exception of:

• :first-child, :focus, :lang
• combinations with pseudo-classes before other selectors

Some differences of style from Internet Explorer and Netscape

When using the Opera browser, you may notice that some pages are displayed differently than in other browsers. In most cases, the differences are caused by errors in the pages that are being displayed. Few Web pages are authored according to W3C's specifications which Opera supports. Opera tries, to some extent, to replicate the errors in browsers from Netscape and Microsoft, but we prioritize implementing the specificaions. For a list of rendering differeces between Opera and Netscape/Microsoft, please read below.

• The color of an HR in Opera is a background property, and Opera accepts all background styles as well as generated content. In NN4 and IE it is a foreground property (color). NN6 does the right thing too (there is a difference between Opera and NN6 if generated content, :before and :after, is used).
• Link underlines can be different in Opera and NN6 than older browsers (the underline one color, the text another). This is a consequence on CSS2 rules on text-decoration.
• IE5/Windows is mistaken in their handling of height and width properties, in effect making Opera (and NN6) boxes appear larger. This is fixed in IE6 in compliant mode.
• IE5 also has an issue with positioning, as a positioned element should be positioned to the nearest containing positioned element, not the containing element.
• Positioning of background images is relative to the element box, not the window. This means that in Opera, a image placed with body{background-position: center center} will be roughly in the middle of a page, not in the middle of the window.
• You would normally want to apply padding to the body element, and not margin (which is the margin between the body and the head/html elements).
• Preformatting of blocklevel content. The allowed content in PRE is inline, not block. This means that content will not be preformatted when a block level element (like a headline) appears, <pre>Pre-formatted<h3>Headline</h3>Not pre-formatted</pre>. In NN and IE <h3>Headline</h3>Not pre-formatted</pre> will be preformatted too.
• Note that while it is possible to style form controls in Opera, you can't make them look like anything other than form controls, eg by setting background color. The CSS specification doesn't require form control widgets to be styleable, and that can be in breach with the operating system UI guidelines. We still plan to support it one day.
• While Netscape 6 is a great leap forward in standards compliance relative to the Netscape 4 series, Mozilla is better. For more information on Mozilla, see the Mozilla site.
• The CSS improvements in IE6 are already implemented in Opera. This means that IE6's display of web pages in standards-compliant mode is much closer to Opera's web page display. For further information, see the Microsoft documentation on IE6.

External Opera CSS conformance charts

This external site offer conformance information on Opera 5: Eric Meyer's Mastergrid.

CSS extensions for XML

Opera 6 uses CSS-like properties to attach information to XML elements that cannot otherwise be represented. Three extension properties have been implemented to allow hyperlinks and images to be included in XML documents. Most often it's better for authors to use XHTML -- rather than the properties described below -- to represent document semantics, but they are described here for reference:

Property:	-set-link-source
Values:	none | attr(<attribute-name>) | content()
Initial:	none
Inherited:	no
Description:	This property sets the value of the 'link' variable which can later be used to generate a link through the 'opera-use-link-source' property.
Property:	-use-link-source
Values:	none | current | next
Initial:	none
Inherited:	no
Description:	This property sets the element to be a source anchor and, if so, declares which value of the 'link' variable that should be used: the current or the next.
Property:	-replace
Values:	none | attr(x)
Initial:	none
Inherited:	no
Description:	This property declares the element to be replaced or not. If replaced, the attr() function is used to point to the attribute where the URI to the content can be found.

In addition Opera accepts a non-standard value for the CSS2 white-space property, namely white-space: -pre-wrap. This value is exactly like white-space: pre with the exception that lines will wrap if wider than the containing box. This is particularily handy for plain-text formats with unpredictable position of line break characters, like e-mail messages. Unlike the other white-space settings however, -pre-wrap will display tab characters like small boxes.

XML support

Opera 6 can parse and display XML documents. Documents with Content-type "text/xml" will be treated as an XML document. If a Content-type is not available, the ".xml" file extension will also make the document be treated as XML.

XML and CSS

In order to display an XML document, a CSS style sheet should be present. Authors can attach style sheets to their XML documents through a processing instruction. Here is a simple example:

<?xml version="1.0"?>
<?xml-stylesheet href="shakespeare.css" type="text/css"?>

If no style sheet is present and the page is not namespaced to HTML, Opera 6 will use the initial values on all CSS properties to display the document. All elements will be inline, and all text will be rendered in the same font.

XSL and XSLT

Opera does not support XSL formatting objects, and neither does it natively support XSLT transformations. XML documents transformed server side will be parsed and displayed by Opera just like any other XML document. For an opinion on client side XSL-FO, see Formatting Objects Considered Harmful.

XML namespaces

Opera 6 supports XML namespaces. The most common use of namespaces is for XHTML processing. From Opera 4, the temporary HTML namespace (http://www.w3.org/TR/REC-html40) is recognized, from Opera 5.1 the XHTML namespace (http://www.w3.org/1999/xhtml) is recognized too.

XHTML support

There are two "modes" of XHTML support, one where the document has the text/html content type and one where it is text/xml, application/xml or application/xhtml+xml. In the first case the document is handles as any other HTML document (giving de facto support for XHTML 1.0, XHTML Basic and XHTML 1.1). In the second case XHTML will be treated as XML with predetermined functionality for HTML elements and attributes. In "XML mode" Opera has the following additional exceptions:

• base
• script and event handlers
• style (use the xml-stylesheet processing instruction instead)

WML 1.2 support

Opera 6.0 supports all Wireless Markup Language (WML) elements, but still lacks support for the following attributes:

• The accesskey and tabindex
• The iname and ivalue for select
• The emptyok and format for input
• The localsrc for img

The rendering of WML documents is controlled with a CSS style sheet called "wml.css" in Opera's installation directory. When editing this file you will need to restart Opera for the changes to take effect.

ECMAScript support

ECMAScript is the standardized version of JavaScript Core. It is being standardized through the ECMA standards body. ECMAScript does not include browser and document related objects, these are specified in a separate document.

Opera 5 supports the entire ECMA-262 2ed standard. It is more or less aligned with JavaScript 1.3. The following items are missing for Opera 6 to have complete JavaScript 1.3 Core support:

1. The Locale methods
2. Complete implementation of the RegExp object
3. Enumeration of built-in objects

Opera also supports most of the ECMA-262 3rd edition that is roughly aligned with Netscape's JavaScript 1.4 Core.

JavaScript environment: DOM and DHTML

The following features are missing from JavaScript 1.3 support:

1. the event variable passed to event handlers does not match the javascript standard
2. cannot set the SRC attribute of iframes

We are currently working on DOM, based on the DOM 2.0 standard. We have also used some of Microsoft's extensions to DOM, notably the method for accessing CSS properties through a style attribute of the HTML elements. Modifying the document structure is not yet possible (ie. you cannot add or remove HTML elements). There are no plans to support Netscape's dynamic layers. Presently, we support getting and setting the following CSS attributes for absolutely positioned HTML elements:

• visibility
• pixelLeft, pixelTop
• pixelWidth, pixelHeight
• zIndex
• color, background (only for setting of colors)

We support the following methods in the document object:

• getElementsByTagName()
• getElementById()
• getElementsByName()

We support the following methods in HTML Elements:

• getElementsByTagName()
• contains()
• parentNode

Support for JavaScript and JScript objects

Described in a separate document. Opera does not support W3C DOM Core apart from the methods mentioned above. Documentation on W3C DOM/HTML support is forthcoming.

Networking protocols support

Opera 6 has full support for HTTP 1.0 and HTTP 1.1. Here are some highlights:

• Persistent connections (multiple request/response through one connection),
• Cachecontrol for no-cache (always check for fresh document) and no-store (don't save to disk),
• Basic Authentication (passwords). Supports Digest Authentication, excepting integrity check on body. No current plans to support NTLM,
• Resume download, provided the server supports it,
• SSL/TLS support (also through proxy/firewall),
• Proxy for HTTP, FTP, Gopher and WAIS.

Encryption: 128 bit encryption (RSA key exchange only) for the Secure Sockets Layer (SSL) versions 2 and 3, and the successor Transport Layer Security (TLS) v1.0. This is supported for HTTP (web), NNTP (news), POP and SMTP (e-mail). Support for generating private keys and submitting certificate requests.

News: simple online newsreader with support for encrypted newsservers and newsserver with passwords. Can decode single article attachments, MIME or uuencoded.

FTP including resume download is supported.

It is possible to download to file for both FTP and HTTP.

Text and internationalization

Unicode support in Opera

Opera can work with all the characters in the Unicode specification. All text communicated to Opera from the network is converted into Unicode.

In order for Opera to render Unicode characters, the needed glyphs have to be available in the fonts on your system. This might be a problem for older Windows systems. For information on available fonts, see Unicode fonts for Windows computers.

Opera 6.0 implements the following writing system related functionality:

• font-switching, needed in order to display characters that the current font does not include.
• line-breaking, needed in order to break scripts written without spaces, such as Chinese, Korean, and Japanese.

Opera relies on the operating system to perform:

• character shaping, contextual glyph selection, ligature forming, character stacking, combining character support etc.

Legacy encoding support

Although Opera works with Unicode (UTF-16), most text on the Internet is encoded in legacy encodings, e.g. ISO 8859-1, Windows-1251, Shift-JIS, EUC-KR. Opera handles this by detecting the character encoding used, and converting it to UTF-16. The user has three options for how to handle these pages.

Auto-detect

In this mode Opera will attempt to detect the encoding used by the page. If the transport protocol provides an encoding name, that is used. If not, Opera will look at the page for a charset declaration. If this is missing, Opera will attempt to auto-detect the encoding, using the domain name to see if the script is a CJK script, and if so which one. Opera can also auto-detect UTF-8.

Writing script auto-detect

In this mode the user can tell that this is a Japanese or Chinese page, but that the encoding is unknown. Opera will then analyze the text in the page to determine which encoding is used.

Encoding override

In this mode the user selects an encoding. This encoding will be used by Opera, regardless of what the page and transport protocol claims is the encoding for the page.

This table shows all the legacy encodings Opera supports in addition to Unicode:

Graphics support

Opera supports GIF89a, JPEG, BMP, WBMP and has full support for PNG including alpha channel (degrees of transparency) and gamma support (device independent colors).