While they might look the same to the human eye, not all spaces are the same. In many contexts, a computer distinguishes between a space and a blank character. This distinction is most important in terms of layout and the way the computer arranges text.
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Effects of a Blank Character
The key difference between the space that you insert by pressing the space bar, and a blank character, is that the latter is usually designated as a non-breaking space. This means a computer handling a block of text knows not to break a line of text between the two words separated by the blank character. Having this extra control can be useful if you want to make sure a string of text remains together on the same line, for example, to aid clarity or visual impact. With websites, a non-breaking space can sometimes make sure non-text elements, such as images, remain side by side.
ASCII codes designate particular characters in a way that can ensure consistency between text handled and displayed by differing applications, operating systems and devices. The ASCII code for a non-breaking space is 255. In many Windows applications that handle text, most notably Microsoft Word, you can use the ASCII code to insert a non-breaking space/blank character by holding down "Alt", typing 255 on your numeric keypad, then releasing "Alt." Note that this won't work if you use the ordinary number keys.
The HTML code for a non-breaking space is "nbsp" (without the quotation marks). You don't need to use any tags to designate a non-breaking space on a Web page. Instead, you simply need to type " " (without the quotation marks) in your HTML code. Many HTML editing applications let you automatically insert this code by choosing "non-breaking space" or a similarly-titled option from an application menu.
Limitations and Restrictions
Try not to overuse blank characters in a document, as this restricts the options for the computer to arrange the line breaks elsewhere in the document. This could lead to breaks that create their own problems with linguistic clarity or visual appeal. On Web pages, excessive use of blank characters can force a page to exceed the display width of some browser/monitor combinations. Blank characters can also cause problems within tables.