Search on specific field is working, search on the page content is less efficient >>> instead use REGEXP

( download the page content:  body.storage.value and match with an REG expression , body is part of _expandable)  

Regular expression and strip html tag

Advanced Searching using CQL

https://developer.atlassian.com/server/confluence/advanced-searching-using-cql/

title="page8"

or

title~"page8"   ( include)

text~ "bla bla bla"  ( include in the content )

https://developer.atlassian.com/server/confluence/cql-field-reference/