What does apply_filters(...) actually do in WordPress?

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I’m trying to understand some of the function in WordPress, but I can’t get my head around what apply_filters(…) actually does.

Is someone able to clear this up for me with a few examples?

NOTE: This question was originally posted at StackOverflow.com by Tim

wordpress api function

Daniel asked 15 years ago
last edited 14 years ago

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- 9 years ago
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Answers (8)

Good Answer

apply_filters($tag, $value) passes the ‘value’ argument to each of the functions ‘hooked’ (using add_filter) into the specified filter ‘tag’. Each function performs some processing on the value and returns a modified value to be passed to the next function in the sequence.

For example, by default (in Wordpress 2.9) the the_content filter passes the value through the following sequence of functions:

wptexturize
convert_smilies
convert_chars
wpautop
shortcode_unautop
prepend_attachment
do_shortcode

NOTE: This answer was originally posted at StackOverflow.com by Richard M

Mike answered 15 years ago
last edited 14 years ago

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Here’s what I’m gleaning, upon considering the most popular answer and additional resources:

$tag seems to be a synonym for the name of the hook. (That’s not particularly intuitive to me.)
the_content is an example of a hook, of the “filter” type.
the_content hook consists of multiple filters.
Filters modify data. They basically filter the database, changing the data before the users view it.
A common use of apply_filters(), for instance, is to apply the_content filters to $content. In this instance, double returns will convert to <p> tags, smiley faces will convert to icons, etc.
“the_content” is a hook, while “the_content()” is a function.

NOTE: This answer was originally posted at StackOverflow.com by Marjorie Roswell

Roger answered 14 years ago

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In the most basic terms, apply_filters is used to initialise a filter hook… add_filter assigns a new function to hooks that have already been created.

NOTE: This answer was originally posted at StackOverflow.com by Steve

John answered 14 years ago

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- 9 years ago
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tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullam