margin, meta, mime

[Margin property] [Math] [Meta tag][Mime types]
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Margin property
See also padding. The margin is a calculated space around any element - a transparent space around any border drawn. Use margin in your stylesheet to remove the need for the deprecated hspace and vspace attributes and to precisely control the relative positioning of page elements. Use margin-top margin-right margin-bottom and margin-left if you want to position the element off center compared to adjacent elements. Setting the margin-left and margin-right to equal values (absolute or relative) will centre the content and text-align:center; will centre the text.

Margin
Border
Padding
Content

Box width
element background
element width

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Math Javascript
- Constants
  Math.E, Math.LN10.
  
  Math.PI, Math.SQRT2.
- Static Functions
  Math.ceil(Math.PI), Math.floor(Math.PI).
  Math.round(Math.PI), Math.round(Math.PI*7).
  Math.cos(30), Math.sin(4/3), Math.tan(2/3). Math.pow(2,3), Math.sqrt(81).
  Math.max(4,3), Math.min(4,3), Math.random().
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Meta tag
Meta tags provide a space for information about your page that would be seen by a search engine and the browser but which is not to be displayed. Content-type definitions, search keywords and descriptions, author and copyright content and certain browser functions can all be within a meta tag. All meta tags must be within the <head> section.
- Page expiry: used by search engine robots to remove expired pages from listing. The content must be a valid time string. Make sure the correct day of the week is specified.
  <meta http-equiv="expires" content="Sat, 31 Dec 2000 21:29:02 GMT">
- Content-type: The server automatically adds content-type:text/html to your HTML document HTTP header (except when you generate a page using CGI). The meta content-type attribute can be extended to include the character set for the document, important to making your page display as expected all over the world.
  <meta http-equiv="content-type" content="text/html; charset=iso-8859-1">
- Client-pull: or forced refresh. You can force the browser to refresh the page after a set number of seconds with a new page or with the current page. (Use with the current page if your content is refreshed by the server at set intervals - e.g. webcams.)
  Same page, wait 15 seconds.
  <meta http-equiv="refresh" content="15">
  New page, wait 5 seconds.
  <meta http-equiv="refresh" content="5; URL=http://next">
- Description: Along with keywords, description is one of the most useful tags for search engines. The description should be plain English, not a string of keywords and you could do worse than simply copy the first 20 to 30 words from the first page on your site. Some search engines object to meta tags and will not use them, so using the same text ensures that your site displays in the same way in the same search on different engines. Search engines that do use the meta tag often insist on only using the meta information. Others only use the first 20 words. Getting the right balance makes a big difference to your ranking.
  <meta name="description" content="A real description of your site that truly reflects the content.">
- Keywords: You should add a list of important search words - the ones you would expect someone to use if they wanted the information your site contains. Again, some engines impose a limit on the number of words (each separated with commas) that will be indexed.
  <meta name="keywords" content="designer, source, advice, help">
- Author: Uses the same syntax as description and keywords; name="author" and content="name"
- Copyright: name="copyright" content="1999 name etc."
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Mime types
The mime-type is the data that links the content with an executing program - like an association in Windows. Setting the correct mime type is vital if your pages are to display correctly, especially with multimedia content. The mime type is normally taken from the file extension and the server and browser both have to be configured to determine how the data is handled. Extended types like Shockwave are supported in the browser using plug-ins that act as the intermediary between the HTML and the browser. Most Internet users only come across mime types when they come across a page that requires a plug-in that is not installed on their system but it is important to remember that each mime type has two parts, one that determines how the server handles the requests and one that is installed on each and every system that browses the page. The same user browsing the same page with two browsers often needs two plugins. Some web designers can find that their carefully constructed pages do not function online because the server does not recognize the mime type - in which case all content of that type is simply ignored. Always check that newer technologies are supported by your ISP or webhost, some may have security implications and your request for support may be denied.

A problem with mime types was uncovered with increasing style sheet usage - some ISP's incorrectly set the .css extension to Continuous Slide Show which means that style sheets fail. The server has been configured to use x-application/css not text/css. CSS is now a registered mime type so this problem should have been solved. If your ISP has not solved this error you may have to change ISP. Using the syntax
<style type="text/css">
should prevent your style sheets being mangled. This attribute is required for correct validation of your CSS anyway.
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