function clbk( error, completions ) {
		var prefix;
		var list;
		var N;

		// Check whether we encountered an error when generating completions...
		if ( error ) {
			debug( 'Encountered an error when generating completions. Unable to display a completion preview.' );
			return;
		}
		list = completions[ 0 ];
		if ( list.length === 0 ) {
			debug( 'Unable to display a completion preview. No completion preview candidates.' );
			self.clear();
			return;
		}
		// Resolve a common prefix from the completion results:
		prefix = commonPrefix( list ); // e.g., [ 'back', 'background', 'backward' ] => 'back'

		// If the completion candidates do not have a common prefix, no completion preview to display, as we do not have a criteria for choosing one candidate over another...
		if ( prefix === '' ) {
			debug( 'Unable to display a completion preview. Completion candidates have no common prefix.' );
			return;
		}
		// Extract the completion preview substring (e.g., if the current line is 'ba', preview should be 'ck'):
		self._preview = prefix.substring( commonPrefix( prefix, completions[ 1 ] ).length ); // eslint-disable-line max-len

		// If the substring is empty, nothing to display...
		if ( self._preview === '' ) {
			debug( 'Unable to display a completion preview. Exact match.' );
			return;
		}
		debug( 'Completion preview: %s', self._preview );

		// Compute the number of characters until the end of the line from the current cursor position:
		N = self._rli.line.length - self._rli.cursor;

		// Move the cursor to the end of the line:
		readline.moveCursor( self._ostream, N );

		// Append the completion preview to the current line (using ASCII color escape codes for displaying grey text):
		self._ostream.write( '\u001b[90m' + self._preview + '\u001b[0m' );

		// Move the cursor back to previous position:
		readline.moveCursor( self._ostream, -self._preview.length-N );
	}
Callback invoked upon resolving potential completion previews.

@private
@param {(Error|null)} error - error object
@param {Array} completions - completion results
@returns {void}