(CNN) Microsoft has made its typographical decree: Two spaces between sentences is too many.

The style choice will now be marked as an error in Microsoft Word -- and users who press the space bar twice after a period will be met with those dreaded blue squiggly lines.

The habit of using two spaces is a relic from the era of typewriters, when typists spaced twice to more clearly define the end of a sentence. Characters were "monospaced" back then, which means they took up the same amount of space on the page -- today, most fonts adjust the width of characters so sentences are easier to read.

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