use ThemePlate\Hook;

// Hook::<ACTION>( <TAG>, <VALUE> )
Hook::append( 'sample_filter', 'ing' );
Hook::prepend( 'sample_filter', 're-' );
Hook::return( 'sample_filter', 'this!' );
Hook::pluck( 'sample_filter', 'i' );
Hook::replace( 'sample_filter', '!', '...' );
Hook::insert( 'sample_filter', 'u', 2 );
Hook::once( 'sample_filter', array( 'pluck', 'th' ) );

^Line by line output with initial value test

ACTION	VALUE	RESULT #1	RESULT #2
append	ing	testing	testing
prepend	re-	re-testing	re-testing
return	this!	this!	this!
pluck	i	ths!	ths!
replace	["!","..."]	ths...	ths...
insert	["u",2]	thus...	thus...
once	["pluck","th"]	us...	thus...

// apply_filters( <TAG>, <INITIAL> );
apply_filters( 'sample_filter', 'test' ); // <RESULT #1>
apply_filters( 'sample_filter', 'test' ); // <RESULT #2>