Where is the identifier notation `anac(h)ronistic' standardized?

[Detlef Lechner]

Hi,

What Unix standard requires to prepend an identifier with a backquote
and terminate it with an apostrophe quote? Example: Synaptic > look up
the DEB program package anacron. The first 2 sentences of its
description are: "Anacron (like `anac(h)ronistic') is a periodic command
scheduler.  It executes commands at intervals specified in days."

Regards,

Detlef Lechner