List of steps to reproduce (step by step, including full links if applicable):

• Have a page with things in triple parentheses (such as w:en:Triple parentheses)
• Link to it and check the page preview

What happens?:
The page preview displays "( )" instead of "(((content)))".

What should have happened instead?:
The page preview should have displayed the full content.
I'm not sure how this should be implemented, but it might be helpful to add something which can disable the removal of content in parentheses (I tried using HTML character codes and putting it in a nowiki tag; neither worked).

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc:
English Wikipedia.

The page preview shows:

Triple parentheses or triple brackets, also known as an ( ), are an antisemitic symbol that has been used to highlight the names of individuals of a Jewish background, or organizations thought to be owned by Jews.

While it should show:

Triple parentheses or triple brackets, also known as an (((echo))), are an antisemitic symbol that has been used to highlight the names of individuals of a Jewish background, or organizations thought to be owned by Jews.