What technology to use for contextual output?

Question

PHP

It is necessary to display a block on the page depending on what word is in the page. If there is a word "children" then we show one block, if there is a word "disease" then another block.
Question: how can this be implemented, what technologies can be used to search for the right words: is the sphinx suitable?
Can this be determined on the fly or will it be necessary to create lists of pages with the necessary words in advance and display certain blocks on them?
PS Why can't I select just the php tag? Only php-fpm, phpmailer or phpbb ))

Answer 1

1. replacing content (HTML markup) via regexp
2. on the client side (js, for example, if you have a widget): dom-parser + ajax; goto 1
is done on the fly....