Docs: improvements for "references - phpdoc - tags - filesource"
Docs: improvements for "references - phpdoc - tags - filesource"

Description
* Split the text in "Description" and "Effects in phpDocumentor".
* Split the text in more paragraphs for improved readability.

Examples:
* Added the PHP open tag to reinforce that the tag can only be used in a file-level PHPDoc.

Other:
* Minor inline markup and grammar fixes.
* Made the syntax outline a code block.

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