Protecting HTML Regions and Other Static Areas |
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In HTML regions and other static display areas, you can reference session state using the &ITEM. notation. Examples of static display areas include HTML regions, page headers and footers, region headers and footers, region titles, button labels, help text, form item labels and post-element text, templates, radiogroup (before and after field text), event success messages, event error messages, navigation bar attributes, application static substitution string values, chart labels and legends, breadcrumbs and list framing text, and calendar text, labels, or legends.
About Safe Item Display Types
When session state is referenced in this way, the value emitted to the page will have special characters (<, >, &, ") escaped if the referenced item is one of the following safe item display types:
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Display as Text (does not save state)
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Display as Text (escape special characters, does not save state)
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Display as Text (based on LOV, does not save state)
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Display as Text (based on PL/SQL, does not save state)
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Text Field (Disabled, does not save state)
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Stop and Start HTML Table (Displays label only)
If the referenced item has a display type other than one of the above types, the value emitted to the page will not have special characters escaped. Although application-level items are also considered to have a safe display type, they do not actually have display properties like form items do.
About the Rules Used to Determine Whether to Escape Values
The Application Express engine uses predefined smart escaping rules to determine if and when to escape values fetched from session state.
The reason for these rules is that items that use the display types listed previously are often for text containing HTML that is intended to be emitted to the browser without being filtered (that is, escaped). The only way this can be made safe is by the enforcement of the rule that these types of items are always escaped on input to the application. For example, if a user passes some text into a safe item using an Oracle Application Express f?p URL syntax, the Application Express engine escapes special characters when saving the value into session state. This has two intended results:
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If the value contained no special characters, the value passed in is saved into session state exactly as it was provided.
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If the value contained special characters, those characters are escaped when the value is saved into session state.
In either situation, the item can now safely be referenced using an &ITEM. notation in any HTML region or other static area mentioned previously.
Using Safe Item Types to Hold and Emit HTML Markup
You can use the safe item types listed previously to hold and emit HTML markup to the browser. For example, suppose you have a requirement to render some text in bold face by referencing a safe page item named P1_XXX (using &P1_XXX.) The item P1_XXX is presumed to contain the following HTML:
<b>ABABABAB</b>
You can achieve this by using application controls (computations, processes, item source expressions, item default values, and so on) to store values into these safe items. When values are introduced in this way, you ensure the safety of the content. When you use these methods, the Application Express engine does not escape any special characters when saving the values into session state.
Finally, the safety of safe items is ensured by a rule that prevents those items from being posted on a page and submitted to the Application Express engine as part of a page submission.