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Christopher Gonzalez
Christopher Gonzalez

Messages Html



In content implemented using markup languages, status messages can be programmatically determined through role or properties such that they can be presented to the user by assistive technologies without receiving focus.




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The intended beneficiaries are blind and low vision users of assistive technologies with screen reader capabilities. An additional benefit is that assistive technologies for users with cognitive disabilities may achieve an alternative means of indicating (or even delaying or supressing) status messages, as preferred by the user.


The scope of this Success Criterion is specific to changes in content that involve status messages. A status message is a defined term in WCAG. There are two main criteria that determine whether something meets the definition of a status message:


Information can be added to pages which does not meet the definition of a status message. For example, the list of results obtained from a search are not considered a status update and thus are not covered by this Success Criterion. However, brief text messages displayed about the completion or status of the search, such as "Searching...", "18 results returned" or "No results returned" would be status updates if they do not take focus. Examples of status messages are given in the section titled Status Message Examples below.


This Success Criterion specifically addresses scenarios where new content is added to the page without changing the user's context. Changes of context, by their nature, interrupt the user by taking focus. They are already surfaced by assistive technologies, and so have already met the goal to alert the user to new content. As such, messages that involve changes of context do not need to be considered and are not within the scope of this Success Criterion. Examples of scenarios that add new content by changing the context are given in the section titled Examples of Changes That Are Not Status Messages below.


The following examples identify situations where no additional author action is necessary. All cases are excepted from this Success Criterion since they do not meet the definition of "status messages."


None of the resulting changes to content meet the definition of status messages. Further, all components that meet the definition of a user interface component already have requirements specified under 4.1.2 Name, Role, Value, including the need to make notifications of changes to values and states available to user agents, including assistive technologies. As a result, changes in state, such as "expanded" or "collapsed," would be announced by the screen reader, and thus the user would be alerted to the 'addition' or 'removal' of content. As such, such content does not need to be addressed by this Success Criterion.


The purpose of this success criterion is not to force authors to generate new status messages. Its intent is to ensure that when status messages are displayed, they are programmatically identified in a way that allows assistive technologies to present them to the user.


Specifies what the origin of this window must be for the event to be dispatched, either as the literal string "*" (indicating no preference) or as a URI. If at the time the event is scheduled to be dispatched the scheme, hostname, or port of this window's document does not match that provided in targetOrigin, the event will not be dispatched; only if all three match will the event be dispatched. This mechanism provides control over where messages are sent; for example, if postMessage() was used to transmit a password, it would be absolutely critical that this argument be a URI whose origin is the same as the intended receiver of the message containing the password, to prevent interception of the password by a malicious third party. Always provide aspecific targetOrigin, not *, if you know where the otherwindow's document should be located. Failing to provide a specific target disclosesthe data you send to any interested malicious site.


If you do expect to receive messages from other sites, always verify thesender's identity using the origin and possibly source properties. Any window (including, for example, ) can send a message to any other window, and you have no guarantees that an unknown sender will not send malicious messages. Having verified identity, however, you still should always verify the syntax ofthe received message. Otherwise, a security hole in the site you trusted to send only trusted messages could then open a cross-site scripting hole in your site.


Any window may access this method on any other window, at any time, regardless of the location of the document in the window, to send it a message. Consequently, any event listener used to receive messages must first check the identity of the sender of the message, using the origin and possibly source properties. This cannot be overstated: Failure to check the originand possibly source properties enables cross-site scriptingattacks.


For IDN host names only, the value of the origin property is not consistently Unicode or punycode; for greatest compatibility check for both the IDN and punycode values when using this property if you expect messages from IDN sites. This value will eventually be consistently IDN, but for now you should handle both IDN and punycode forms.


It is not possible for content or web context scripts to specify a targetOrigin to communicate directly with an extension (either the background script or a content script). Web or content scripts can use window.postMessage with a targetOrigin of "*" to broadcast to every listener, but this is discouraged, since an extension cannot be certain the origin of such messages, and other listeners (including those you do not control) can listen in.


\n Specifies what the origin of this window must be for the event to be\n dispatched, either as the literal string \"*\" (indicating no preference)\n or as a URI. If at the time the event is scheduled to be dispatched the scheme,\n hostname, or port of this window's document does not match that provided\n in targetOrigin, the event will not be dispatched; only if all three\n match will the event be dispatched. This mechanism provides control over where\n messages are sent; for example, if postMessage() was used to transmit a\n password, it would be absolutely critical that this argument be a URI whose origin is\n the same as the intended receiver of the message containing the password, to prevent\n interception of the password by a malicious third party. Always provide a\nspecific targetOrigin, not *, if you know where the other\nwindow's document should be located. Failing to provide a specific target discloses\nthe data you send to any interested malicious site.\n


\n If you do expect to receive messages from other sites, always verify the\nsender's identity using the origin and possibly\n source properties. Any window (including, for example,\n ) can send a message to any other window,\n and you have no guarantees that an unknown sender will not send malicious messages.\n Having verified identity, however, you still should always verify the syntax of\nthe received message. Otherwise, a security hole in the site you trusted to\n send only trusted messages could then open a cross-site scripting hole in your site.\n


\n Any window may access this method on any other window, at any time, regardless of the\n location of the document in the window, to send it a message. Consequently, any event\n listener used to receive messages must first check the identity of the\n sender of the message, using the origin and possibly source\n properties. This cannot be overstated: Failure to check the origin\nand possibly source properties enables cross-site scripting\nattacks.\n


\n For IDN host names only, the value of the origin property is not\n consistently Unicode or punycode; for greatest compatibility check for both the IDN and\n punycode values when using this property if you expect messages from IDN sites. This\n value will eventually be consistently IDN, but for now you should handle both IDN and\n punycode forms.\n


\n It is not possible for content or web context scripts to specify a\n targetOrigin to communicate directly with an extension (either the\n background script or a content script). Web or content scripts can use\n window.postMessage with a targetOrigin of \"*\" to\n broadcast to every listener, but this is discouraged, since an extension cannot be\n certain the origin of such messages, and other listeners (including those you do not\n control) can listen in.\n


For this, Django provides full support for cookie- and session-basedmessaging, for both anonymous and authenticated users. The messages frameworkallows you to temporarily store messages in one request and retrieve them fordisplay in a subsequent request (usually the next one). Every message istagged with a specific level that determines its priority (e.g., info,warning, or error).


This class stores the message data in a cookie (signed with a secret hashto prevent manipulation) to persist notifications across requests. Oldmessages are dropped if the cookie data size would exceed 2048 bytes.


The messages framework is based on a configurable level architecture similarto that of the Python logging module. Message levels allow you to groupmessages by type so they can be filtered or displayed differently in views andtemplates.


Due to the way cookies (and hence sessions) work, the behavior of anybackends that make use of cookies or sessions is undefined when the sameclient makes multiple requests that set or get messages in parallel. Forexample, if a client initiates a request that creates a message in one window(or tab) and then another that fetches any uniterated messages in anotherwindow, before the first window redirects, the message may appear in thesecond window instead of the first window where it may be expected. 041b061a72


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