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Saturday 16 August 2008

HTML Interview Questions and Answers 10

When I try to upload my site, all my images are X's. How do I get them to load correctly?
They are a few reasons that this could happen. The most common are:

1. You're attempting to use a .bmp or .tif or other non-supported file format. You can only use .gif and .jpg on the web. You must convert files that are not .gif or .jpg into a .gif or .jpg with your image/graphics program.
2. You've forgotten to upload the graphic files. Double-Check.
3. You've incorrectly linked to the images. When you are starting out, try just using the file name in the tag. If you have cat.jpg, use
img src="cat.jpg">.
4. Image file names are case-sensitive. If your file is called CaT.JpG, you cannot type cat.jpg, you must type CaT.JpG exactly in the src.
5. If all of the above fail, re-upload the image in BINARY mode. You may have accidentally uploaded the image in ASCII mode.

Is there a site that shows which tags work on which browsers?
There have been several attempts to do this, but I'm not aware of any really good source of comparisons between the browsers. The trouble is that there are many different versions of each browser, and many different tags. All current browsers should support the tags in the official HTML 3.2 specification, but the major ones also support nonstandard tags and sometimes have slightly different implementations. One place that has fairly good compatibility info is Browsercaps.

Why does the browser show my plain HTML source?
If Microsoft Internet Explorer displays your document normally, but other browsers display your plain HTML source, then most likely your web server is sending the document with the MIME type "text/plain". Your web server needs to be configured to send that filename with the MIME type "text/html". Often, using the filename extension ".html" or ".htm" is all that is necessary. If you are seeing this behavior while viewing your HTML documents on your local Windows filesystem, then your text editor may have added a ".txt" filename extension automatically. You should rename filename.html.txt to filename.html so that Windows will treat the file as an HTML document.

How can I display an image on my page?
Use an IMG element. The SRC attribute specifies the location of the image. The ALT attribute provides alternate text for those not loading images. For example:

ACME Products

Why do my links open new windows rather than update an existing frame?
If there is no existing frame with the name you used for the TARGET attribute, then a new browser window will be opened, and this window will be assigned the name you used. Furthermore, TARGET="_blank" will open a new, unnamed browser window.
In HTML 4, the TARGET attribute value is case-insensitive, so that abc and ABC both refer to the same frame/window, and _top and _TOP both have the same meaning. However, most browsers treat the TARGET attribute value as case-sensitive and do not recognize ABC as being the same as abc, or _TOP as having the special meaning of _top.
Also, some browsers include a security feature that prevents documents from being hijacked by third-party framesets. In these browsers, if a document's link targets a frame defined by a frameset document that is located on a different server than the document itself, then the link opens in a new window instead.

How do I get out of a frameset?
If you are the author, this is easy. You only have to add the TARGET attribute to the link that takes readers to the intended 'outside' document. Give it the value of _top.
In many current browsers, it is not possible to display a frame in the full browser window, at least not very easily. The reader would need to copy the URL of the desired frame and then request that URL manually.
I would recommend that authors who want to offer readers this option add a link to the document itself in the document, with the TARGET attribute set to _top so the document displays in the full window if the link is followed.

How do I make a frame with a vertical scrollbar but without a horizontal scrollbar?
The only way to have a frame with a vertical scrollbar but without a horizontal scrollbar is to define the frame with SCROLLING="auto" (the default), and to have content that does not require horizontal scrolling. There is no way to specify that a frame should have one scrollbar but not the other. Using SCROLLING="yes" will force scrollbars in both directions (even when they aren't needed), and using SCROLLING="no" will inhibit all scrollbars (even when scrolling is necessary to access the frame's content). There are no other values for the SCROLLING attribute.

Are there any problems with using frames?
The fundamental problem with the design of frames is that framesets create states in the browser that are not addressable. Once any of the frames within a frameset changes from its default content, there is no longer a way to address the current state of the frameset. It is difficult to bookmark - and impossible to link or index - such a frameset state. It is impossible to reference such a frameset state in other media. When the sub-documents of such a frameset state are accessed directly, they appear without the context of the surrounding frameset. Basic browser functions (e.g., printing, moving forwards/backwards in the browser's history) behave differently with framesets. Also, browsers cannot identify which frame should have focus, which affects scrolling, searching, and the use of keyboard shortcuts in general.
Furthermore, frames focus on layout rather than on information structure, and many authors of framed sites neglect to provide useful alternative content in the NOFRAMES element. Both of these factors cause accessibility problems for browsers that differ significantly from the author's expectations and for search engines.

Do search engines dislike frames?
Search engines can link directly to framed content documents, but they cannot link to the combinations of frames for which those content documents were designed. This is the result of a fundamental flaw in the design of frames.
Search engines try to provide their users with links to useful documents. Many framed content documents are difficult to use when accessed directly (outside their intended frameset), so there is little benefit if search engines offer links to them. Therefore, many search engines ignore frames completely and go about indexing more useful (non-framed) documents.
Search engines will index your

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