Paragraph breaks set a rhythm for the reader. The breaks have a relationship with the column of text as well as the page margins. A break may be introduced as an indentation, as a space or both. The over all page feel will be influenced by your choice.
Definitions: In typography there are 4 rules regarding paragraph breaks: first line at the beginning of an article should be flush left (do not indent first paragraph) block paragraphs are flush left and are separated by extra leading not a full return the amount indent is = to the leading (sometimes needs a bit more) never hit two returns between paragraphs
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