By clicking sign up, you agree to receive emails from Techopedia and agree to our Terms of Use and Privacy Policy. HTML defines how a Web browser displays every browser page element, including pictures, text, hyperlinks and many others. Sometimes you'll see an HTML file as ".
File extensions, such as htm, are almost always three letters and usually lower case. Other common extensions include the following the file called example:. The extensions may be derived from the file's function, creator, company or some other associated word or action. In the absence of a user preference, the default should be navigation if the element has no download attribute, and should be to download the specified resource if it does.
Whether determined by the user's preferences or via the presence or absence of the attribute, if the decision is to use the hyperlink for navigation then the user agent must follow the hyperlink , and if the decision is to use the hyperlink to download a resource, the user agent must download the hyperlink.
These terms are defined in subsequent sections below. The download attribute, if present, indicates that the author intends the hyperlink to be used for downloading a resource. The attribute may have a value; the value, if any, specifies the default filename that the author recommends for use in labeling the resource in a local file system. There are no restrictions on allowed values, but authors are cautioned that most file systems have limitations with regard to what punctuation is supported in filenames, and user agents are likely to adjust filenames accordingly.
The value is used by the user agent for hyperlink auditing. The rel attribute on a and area elements controls what kinds of links the elements create. The attribute's value must be an unordered set of unique space-separated tokens. The allowed keywords and their meanings are defined below.
The possible supported tokens are noreferrer , noopener , and opener. The rel attribute has no default value. If the attribute is omitted or if none of the values in the attribute are recognized by the user agent, then the document has no particular relationship with the destination resource other than there being a hyperlink between the two. The hreflang attribute on a elements that create hyperlinks , if present, gives the language of the linked resource.
It is purely advisory. The value must be a valid BCP 47 language tag. The type attribute, if present, gives the MIME type of the linked resource. The value must be a valid MIME type string. User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use metadata included in the link to the resource to determine its type.
The referrerpolicy attribute is a referrer policy attribute. Its purpose is to set the referrer policy used when following hyperlinks. It is initially null. If this element's href content attribute is absent, set this element's url to null. Otherwise, parse this element's href content attribute value relative to this element's node document. If parsing is successful, set this element's url to the result; otherwise, set this element's url to null.
When elements implementing the HTMLHyperlinkElementUtils mixin are created, and whenever those elements have their href content attribute set, changed, or removed, the user agent must set the url. If element's url is non-null, its scheme is " blob ", and it has an opaque path , then terminate these steps. Set the url. To update href , set the element's href content attribute's value to the element's url , serialized.
The href getter steps are:. Reinitialize url. Let url be this 's url. If url is null and this has no href content attribute, return the empty string.
Otherwise, if url is null, return this 's href content attribute's value. Return url , serialized. The href setter steps are to set this 's href content attribute's value to the given value.
The origin getter steps are:. If this 's url is null, return the empty string. Return the serialization of this 's url 's origin. The protocol getter steps are:.
If this 's url is null, return " : ". Return this 's url 's scheme , followed by " : ". The protocol setter steps are:. If this 's url is null, then return. Basic URL parse the given value, followed by " : ", with this 's url as url and scheme start state as state override.
Because the URL parser ignores multiple consecutive colons, providing a value of " https: " or even " https " is the same as providing a value of " https ". Update href. The username getter steps are:. Return this 's url 's username. The username setter steps are:. Set the username , given url and the given value. The password getter steps are:. If url is null, then return the empty string. Return url 's password. The password setter steps are:. Set the password , given url and the given value.
The host getter steps are:. If url or url 's host is null, return the empty string. If url 's port is null, return url 's host , serialized. Return url 's host , serialized , followed by " : " and url 's port , serialized. The host setter steps are:. If url is null or url has an opaque path , then return. Basic URL parse the given value, with url as url and host state as state override. The hostname getter steps are:.
Return url 's host , serialized. The hostname setter steps are:. Basic URL parse the given value, with url as url and hostname state as state override. The port getter steps are:. If url or url 's port is null, return the empty string. Return url 's port , serialized. The port setter steps are:. If the given value is the empty string, then set url 's port to null. Otherwise, basic URL parse the given value, with url as url and port state as state override.
The pathname getter steps are:. Return the result of URL path serializing url. The pathname setter steps are:. Set url 's path to the empty list. Basic URL parse the given value, with url as url and path start state as state override. The search getter steps are:. If url is null, or url 's query is either null or the empty string, return the empty string. Return "? The search setter steps are:.
If url is null, terminate these steps. If the given value is the empty string, set url 's query to null. Let input be the given value with a single leading "? Set url 's query to the empty string. Basic URL parse input , with null, this element's node document 's document's character encoding , url as url , and query state as state override. The hash getter steps are:. If url is null, or url 's fragment is either null or the empty string, return the empty string.
Return " ", followed by url 's fragment. The hash setter steps are:. If url is null, then return. If the given value is the empty string, set url 's fragment to null. Let input be the given value with a single leading " " removed, if any. Set url 's fragment to the empty string. Basic URL parse input , with url as url and fragment state as state override. This is also used by form submission for the form element. The exception for a elements is for compatibility with web content.
To get an element's noopener , given an a , area , or form element element and a string target :. If element 's link types include the noopener or noreferrer keyword, then return true.
Return false. To follow the hyperlink created by an element subject , given an optional hyperlinkSuffix default null :.
If subject cannot navigate , then return. Let replace be false. Let source be subject 's node document 's browsing context. Let targetAttributeValue be the empty string. If subject is an a or area element, then set targetAttributeValue to the result of getting an element's target given subject.
Let noopener be the result of getting an element's noopener with subject and targetAttributeValue. Let target and windowType be the result of applying the rules for choosing a browsing context given targetAttributeValue , source , and noopener.
If target is null, then return. Parse a URL given subject 's href attribute, relative to subject 's node document. Otherwise, if parsing the URL failed, the user agent may report the error to the user in a user-agent-specific manner, may queue an element task on the DOM manipulation task source given subject to navigate the target browsing context to an error page to report the error, or may ignore the error and do nothing.
In any case, the user agent must then return. If hyperlinkSuffix is non-null, then append it to URL. Let request be a new request whose URL is URL and whose referrer policy is the current state of subject 's referrerpolicy content attribute.
If subject 's link types includes the noreferrer keyword, then set request 's referrer to " no-referrer ". Let historyHandling be " replace " if windowType is not " existing or none "; otherwise, " default ".
Unlike many other types of navigations, following hyperlinks does not have special " replace " behavior for when documents are not completely loaded. This is true for both user-initiated instances of following hyperlinks, as well as script-triggered ones via, e. Queue an element task on the DOM manipulation task source given subject to navigate target to request with historyHandling set to historyHandling and the source browsing context set to source.
To indicate that a resource is intended to be downloaded for use later, rather than immediately used, the download attribute can be specified on the a or area element that creates the hyperlink to that resource. The attribute can furthermore be given a value, to specify the filename that user agents are to use when storing the resource in a file system.
This is to protect users from being made to download sensitive personal or confidential information without their full understanding. The following allowed to download algorithm takes an initiator browsing context and an instantiator browsing context , and returns a boolean indicating whether or not downloading is allowed:.
If the initiator browsing context 's sandboxing flags has the sandboxed downloads browsing context flag set, then return false. If the instantiator browsing context is non-null, and its sandboxing flags has the sandboxed downloads browsing context flag set, then return false.
Optionally, the user agent may return false, if it believes doing so would safeguard the user from a potentially hostile download. Return true. To download the hyperlink created by an element subject , given an optional hyperlinkSuffix default null :. Run the allowed to download algorithm with the subject 's node document 's browsing context and null. If the algorithm returns false, then return.
If parsing the URL fails, the user agent may report the error to the user in a user-agent-specific manner, may navigate to an error page to report the error, or may ignore the error and do nothing. In either case, the user agent must return. Run these steps in parallel :. Let request be a new request whose URL is URL , client is entry settings object , initiator is " download ", destination is the empty string, and whose synchronous flag and use-URL-credentials flag are set.
Handle the result of fetching request as a download. When a user agent is to handle a resource obtained from a fetch as a download , it should provide the user with a way to save the resource for later use, if a resource is successfully obtained.
Otherwise, it should report any problems downloading the file to the user. If the user agent needs a filename for a resource being handled as a download , it should select one using the following algorithm.
This algorithm is intended to mitigate security dangers involved in downloading files from untrusted sites, and user agents are strongly urged to follow it.
Let filename be the undefined value. Let resource origin be the origin of the URL of the resource being downloaded, unless that URL's scheme component is data , in which case let resource origin be the same as the interface origin , if any. If there is no interface origin , then let trusted operation be true. Otherwise, let trusted operation be true if resource origin is the same origin as interface origin , and false otherwise.
Let proposed filename have the value of the download attribute of the element of the hyperlink that initiated the download at the time the download was initiated. If trusted operation is true, let filename have the value of proposed filename , and jump to the step labeled sanitize below. Let filename be set to the user's preferred filename or to a filename selected by the user agent, and jump to the step labeled sanitize below. If the algorithm reaches this step, then a download was begun from a different origin than the resource being downloaded, and the origin did not mark the file as suitable for downloading, and the download was not initiated by the user.
This could be because a download attribute was used to trigger the download, or because the resource in question is not of a type that the user agent supports.
This could be dangerous, because, for instance, a hostile server could be trying to get a user to unknowingly download private information and then re-upload it to the hostile server, by tricking the user into thinking the data is from the hostile server. Thus, it is in the user's interests that the user be somehow notified that the resource in question comes from quite a different source, and to prevent confusion, any suggested filename from the potentially hostile interface origin should be ignored.
Sanitize : Optionally, allow the user to influence filename. For example, a user agent could prompt the user for a filename, potentially providing the value of filename as determined above as a default value. Adjust filename to be suitable for the local file system. For example, this could involve removing characters that are not legal in filenames, or trimming leading and trailing whitespace. If the platform conventions do not in any way use extensions to determine the types of file on the file system, then return filename as the filename.
Let claimed type be the type given by the resource's Content-Type metadata , if any is known. Let named type be the type given by filename 's extension , if any is known. For the purposes of this step, a type is a mapping of a MIME type to an extension. If named type is consistent with the user's preferences e. If claimed type and named type are the same type i. If the claimed type is known, then alter filename to add an extension corresponding to claimed type. Otherwise, if named type is known to be potentially dangerous e.
This last step would make it impossible to download executables, which might not be desirable. As always, implementers are forced to balance security and usability in this matter. Return filename as the filename. For the purposes of this algorithm, a file extension consists of any part of the filename that platform conventions dictate will be used for identifying the type of the file.
For example, many operating systems use the part of the filename following the last dot ". User agents should ignore any directory or path information provided by the resource itself, its URL , and any download attribute, in deciding where to store the resulting file in the user's file system. If a hyperlink created by an a or area element has a ping attribute, and the user follows the hyperlink, and the value of the element's href attribute can be parsed , relative to the element's node document , without failure, then the user agent must take the ping attribute's value, split that string on ASCII whitespace , parse each resulting token relative to the element's node document , and then run these steps for each resulting URL record ping URL , ignoring tokens that fail to parse:.
Optionally, return. For example, the user agent might wish to ignore any or all ping URLs in accordance with the user's expressed preferences.
Fetch request. This may be done in parallel with the primary fetch, and is independent of the result of that fetch. Based on the user's preferences, UAs may either ignore the ping attribute altogether, or selectively ignore URLs in the list e. User agents must ignore any entity bodies returned in the responses.
User agents may close the connection prematurely once they start receiving a response body. When the ping attribute is present, user agents should clearly indicate to the user that following the hyperlink will also cause secondary requests to be sent in the background, possibly including listing the actual target URLs.
For example, a visual user agent could include the hostnames of the target ping URLs along with the hyperlink's actual URL in a status bar or tooltip. The ping attribute is redundant with pre-existing technologies like HTTP redirects and JavaScript in allowing web pages to track which off-site links are most popular or allowing advertisers to track click-through rates.
However, the ping attribute provides these advantages to the user over those alternatives:. Thus, while it is possible to track users without this feature, authors are encouraged to use the ping attribute so that the user agent can make the user experience more transparent. This table is non-normative; the actual definitions for the link types are given in the next few sections.
In this section, the term referenced document refers to the resource identified by the element representing the link, and the term current document refers to the resource within which the element representing the link finds itself. To determine which link types apply to a link , a , area , or form element, the element's rel attribute must be split on ASCII whitespace.
The resulting tokens are the keywords for the link types that apply to that element. Except where otherwise specified, a keyword must not be specified more than once per rel attribute.
Some of the sections that follow the table below list synonyms for certain keywords. The indicated synonyms are to be handled as specified by user agents, but must not be used in documents for example, the keyword " copyright ". Keywords that are body-ok affect whether link elements are allowed in the body. The body-ok keywords are dns-prefetch , modulepreload , pingback , preconnect , prefetch , preload , prerender , and stylesheet.
New link types that are to be implemented by web browsers are to be added to this standard. The remainder can be registered as extensions. Chrome Android? WebView Android? Samsung Internet? Opera Android? The alternate keyword may be used with link , a , and area elements. The alternate keyword modifies the meaning of the stylesheet keyword in the way described for that keyword.
The alternate keyword does not create a link of its own. Here, a set of link elements provide some style sheets:. The keyword creates a hyperlink referencing a syndication feed though not necessarily syndicating exactly the same content as the current page. If the user agent has the concept of a default syndication feed, the first such element in tree order should be used as the default. The following link elements give syndication feeds for a blog:.
Such link elements would be used by user agents engaged in feed autodiscovery, with the first being the default where applicable. The following example offers various different syndication feeds to the user, using a elements:. The keyword creates a hyperlink referencing an alternate representation of the current document. The nature of the referenced document is given by the hreflang , and type attributes.
If the alternate keyword is used with the hreflang attribute, and that attribute's value differs from the document element 's language , it indicates that the referenced document is a translation. If the alternate keyword is used with the type attribute, it indicates that the referenced document is a reformulation of the current document in the specified format.
The hreflang and type attributes can be combined when specified with the alternate keyword. The following example shows how you can specify versions of the page that use alternative formats, are aimed at other languages, and that are intended for other media:.
This relationship is transitive — that is, if a document links to two other documents with the link type " alternate ", then, in addition to implying that those documents are alternative representations of the first document, it is also implying that those two documents are alternative representations of each other.
The author keyword may be used with link , a , and area elements. This keyword creates a hyperlink. For a and area elements, the author keyword indicates that the referenced document provides further information about the author of the nearest article element ancestor of the element defining the hyperlink, if there is one, or of the page as a whole, otherwise. For link elements, the author keyword indicates that the referenced document provides further information about the author for the page as a whole.
The "referenced document" can be, and often is, a mailto: URL giving the email address of the author. Synonyms : For historical reasons, user agents must also treat link , a , and area elements that have a rev attribute with the value " made " as having the author keyword specified as a link relationship.
The bookmark keyword may be used with a and area elements. The bookmark keyword gives a permalink for the nearest ancestor article element of the linking element in question, or of the section the linking element is most closely associated with , if there are no ancestor article elements.
The following snippet has three permalinks. A user agent could determine which permalink applies to which part of the spec by looking at where the permalinks are given. The canonical keyword may be used with link element.
That helps search engines reduce duplicate content, as described in more detail in The Canonical Link Relation. The dns-prefetch keyword may be used with link elements.
This keyword creates an external resource link. This keyword is body-ok. The dns-prefetch keyword indicates that preemptively performing DNS resolution for the origin of the specified resource is likely to be beneficial, as it is highly likely that the user will require resources located at that origin , and the user experience would be improved by preempting the latency costs associated with DNS resolution.
User agents must implement the processing model of the dns-prefetch keyword described in Resource Hints. There is no default type for resources given by the dns-prefetch keyword. The external keyword may be used with a , area , and form elements. Subscribe to the daily or weekly newsletter and get featured terms and quizzes delivered to your inbox.
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Below is an example of a basic web page written in HTML with a description of each section and its function. The box above contains the key ingredients to a basic web page. Each of the lines are explained below in further detail. It uses the same basic rules as HTML4, but adds some new tags and attributes which allow for better semantics and for dynamic elements that are activated using JavaScript.
There are also new input types for forms , which include tel, search, url, e-mail, datetime, date, month, week, time, datetime-local, number, range, and color. With the increasing movement to keep structure and style separate, some styling elements were removed. Also tags with accessibility issues or saw very little use were also removed. HTML5 also simplifies the doctype declaration to the tag in the following box. Because HTML is a markup language, it can be created and viewed in any text editor if saved with a.
Once the HTML file is created, it can be viewed locally or uploaded to a web server to be viewed online using a browser.
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