Markup guidelines
One of the goals in writing portlet markup is to provide a consistent,
clean, and complete user interface. The portal server page is displayed using skins and themes defined
by the portal designer or administrator. For portlets to appear integrated
with an organization's portal or user's customized portal, they should generate
markup that invokes the generic style classes for portlets, rather than using
tags or attributes to specify colors, fonts, or other visual elements. See Portal style classes for more information.
This section provides information for using HTML, WML, and cHTML markup
in your portlet JSPs. Portlets are allowed to render only markup fragments,
which are then assembled by the portlet framework for a complete page. Portlet
output should contain complete, well-structured, and valid markup fragments.
This helps to prevent the portlet's HTML code, for example, from corrupting
the portal's aggregated HTML code. You should use a validation tool for your
markup, such as the W3C
HTML Validation Service or a tool from a markup editor.
These guidelines are based on the JSP coding guidelines for standard portlets
and for IBM portlets. See the corresponding best practices guide for the type
of portlet you are developing on the WebSphere Portal Zone for complete information about
portlet output guidelines.
HTML
- Use standard HTML. For the official HTML specification, see http://www.w3.org.
- Use only HTML fragments. Because portlets contribute to the content of
a larger page, they should only provide HTML fragments and should not have
<html>, <head>, or <body> tags.
- Use only elements that can be rendered properly in an HTML table cell
(<td>...</td>). Frames, for example, do not appear when inserted in
a table.
- Make sure the fragments are well-formed to prevent unbalanced pages.
Watch out for unterminated, extraneous, or improperly nested tags. The behavior
of pages with improperly terminated tags is unpredictable.
- Avoid deeply nested tables as they make performance
slower on older Netscape browsers.
- Avoid lengthy, complex HTML. Portlets share a page with others and the
more content each portlet generates, the more the browser has to process
before it can display anything.
- Use portlet classes in the portal server's style sheet, Styles.css.
If you hard code the fonts and colors, the portlet's appearance will look
out of place when the user changes the page style settings. Portal administrators
and users can affect the appearance of the portal by changing the portal
theme and the portlet skins. Portlets can pick up on style changes by using
styles defined in the portal theme's cascading style sheet (Styles.css).
For example, instead of decorating an <input> element with the style attribute,
refer to the theme's input class definition: <inputclass="portlet-form-button"
type="submit">
Portlet style classes are marked with the following comment:
/* Styles used in portlets
This section of
the style sheet has a mixture of classic IBM style classes and the standard
WSRP style classes. When available, use the WSRP style classes, which are
prepended with a portlet- prefix. See CSS Style Definitions in
the WSRP specification.
- Do not use CSS for absolute positioning. This could defeat the portal
features that allow users and administrators to place content on the page.
- Limit the size of the portlet output. Portlets contribute a portion of
a larger page. The size of the JSPs (in terms of horizontal and vertical
span) can determine how easily the portlet can fit on a page with multiple
columns and other portlets. A large portlet forces other portlets off the
screen and creates large scrolling regions, resulting in usability issues.
Therefore, when designing a portlet's JSPs, avoid unnecessary layout elements,
focus the portlet's view on the pertinent information, and consider whether
the portlet is intended to be placed on pages with other portlets. In particular,
take notice of image size, pre-formatted text (<pre/> tag), and absolute
widths on elements, such as tables.
- Use Java style comments instead of HTML style. HTML comments remain in
the rendered content, adding to the document size and the amount of data
that passes to the client. If you use Java style comments within your JSPs,
instead, they are removed from the rendered source, along with the rest of
the Java code. You must imbed these comments within scriptlets:
<% // this is a comment %>
- Make pages fully accessible. To allow portal users with disabilities to
be able to use your portlet, the JSPs should be fully enabled for keyboard-only
control and other assistive technologies. Follow these general guidelines:
- Use the alt attribute with images to define descriptive
text of the image content.
- Use <label> tags to associate labels with form input controls, so that
page readers will be able to associate prompts with inputs.
- Do not use color alone to denote state or information. For example, using
red to emphasize text does not help those who are color blind. Use bold or
italics instead, or use color in conjunction with graphic changes.
- Do not use voice or other sounds to convey information.
See the IBM
Accessibility Center for more information.
- URIs, HTML element name attributes, and JavaScript resources must be namespace
encoded. Use <portlet:namespace/> (standard portlet API) or <portletAPI:encodeNamespace
value="function" /> (IBM portlet API) for named elements
to prevent name conflicts with other portlets on the portal page.
- Test the portlet output in different browsers. Check portlet behavior
when resizing the page to ensure that your portlet works with different browser
sizes. Check portlet behavior when the default browser font is changed; your
portlet should handle these situations seamlessly.
- Do not draw portlet banners, such as title bars, as they are provided
by the portal aggregation.
- Minimize dependencies on JavaScript. Because JavaScript implementations
and behavior differ widely among browser types and versions, the more your
portlet depends on JavaScript, the more browser-dependent your portlet becomes.
Additionally, the more of the page that is rendered using JavaScript, the
more difficult it is to maintain and to extend to markups other than HTML.
Also, it is more difficult to namespace encode JavaScript resources and nearly
impossible to properly encode (response.encodeUrl()) URLs built using JavaScript.
- Do not use pop-ups. Interactions within the portal are state-based, which
means that the portal tracks your trail through the pages and portlets. Using
the browser's back button, or creating pop-up browser instances containing
portlets, can cause the portal to lose track of your current state and cause
problems. Other than using JavaScript prompts, there is no safe way to spawn
pop-ups within the portal, unless the new link takes you to an external page,
outside the portal. The alternative is to link to an external page within
a new browser window (using the TARGET attribute on the anchor), so that
the user is left within the portal in the original browser window.
- Use IFRAMEs with caution. IFRAMEs are an easy way to include external
content within a portlet, but undermine the whole portlet principle because
the portlet API is just tunneled or side-stepped. Therefore, IFRAMEs should
only be used for very special cases, such as surfacing legacy applications.
Other potential issues to consider when using an IFRAME are:
- The IFRAME fills its content based on a URL. The URL must be addressable
by the browser, therefore the server that is the target of the URL must be
accessible by the browser.
- Not all browser levels support IFRAMEs.
- If the content is larger than the IFRAME region, then enable horizontal
and vertical scrolling to let the user scroll through the embedded content.
Content which contains scrolling regions itself can make it difficult for
the end user to manipulate all scrolling regions to view all embedded content,
causing usability problems.
- Use JSTL instead of re-inventing common tags. The Java Standard Tag Library
(JSTL) defines many commonly needed tags for conditions, iterations, URLs,
internationalization and formatting. See Using
JSTL in portlet JSPs for more information.
WML
- Use standard WML. For information, refer to http://www.wapforum.org.
- When designing your portlet, assume that it could be displayed alone or
with other portlets.
- Watch out for unterminated and extraneous tags; the behavior of pages
with improperly terminated tags is undefined.
- Use only elements that can be included into a card (probably together
with other portlets and elements) and do not create separate cards.
- Do not set the card title.
- Do not use templates.
- Avoid lengthy, complex WML as the buffer length can be restricted by the
user agent and portlets may share a page with others.
- Avoid using images too often. When using images, define a meaningful alt name,
as this is necessary for the devices that do not support images, or if the
image cannot be fetched. If possible, define localsrc.
- Do not use intrinsic events as these events (such as oneventforward and
oneventbackward) may be added only by the aggregation level.
- Avoid using timers.
- Use user-triggered events only if necessary, and always define label and
name parameters explicitly. Prefix the name with the portlet's unique identifier,
otherwise conflict is possible between different portlets on one page. Use
meaningful names for labels.
- Do not create fixed-width WML tables or images in portlets.
- Avoid long, unbroken lines of unwrapped text to help prevent unnecessary
scrolling.
Compact HTML (cHTML)
- Use standard cHTML. For information on i-mode compatible HTML, refer to Compact HTML for Small Information Appliances.
- Assume when designing your portlet that it could be displayed alone or
with other portlets.
- Watch out for unterminated, extraneous, or improperly nested tags. The
behavior of pages with improperly terminated tags is unpredictable.
- Use only elements that can be included into a body; do not use <head> or <body> tags.
- Avoid lengthy, complex cHTML as portlets may share a page with others.
- Avoid using images too often and do not use alignment and positioning
parameters with images.
- Do not exceed a length of 24 symbols for the phone numbers used as references
in the <a> tag.
- Do not use URLs that are longer than 200 bytes.
Parent topic: Portlet development reference
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