Unknown method process.openStdin() - node.js

Question

I'm trying to pipe grep results into nodejs script. I've found, that I should receive data from process.stdin.
Also I've found several ways to work with stdin. But they are different and I can't find all information about it. I know four ways (first 3 start with var data = ""):
1) Most popular in search results
process.stdin.resume();
process.stdin.setEncoding( 'utf8' );
process.stdin.on('data', function(chunk) { data += chunk; });
process.stdin.on('end', function() { console.log('data: ' + data); });
2) Looks like the first one, but with unknown function process.openStdin()
var stdin = process.openStdin();
stdin.on('data', function(chunk) { data += chunk; });
stdin.on('end', function() { console.log('data: ' + data); });
3) In the documentation I've read that calling stdin.resume() changes stdin to 'old type'. So if we didn't called 'resume' - we can use 'readable' event
process.stdin.setEncoding('utf8');
process.stdin.on('readable', function() { data += process.stdin.read(); });
process.stdin.on('end', function() { console.log('data: ' + data); });
4) Use module readline. It is very usefull as long as grep results are in mutiple lines and there I don't need to split received data by myself. But for a long time i couldn't understand why all information is piped to stdout directly. Then i i've found that we can pass empty object instead of process.stdout while creating interface and data wouldn't piped to output.
var readline = require('readline'),
//rl = readline.createInterface(process.stdin, process.stdout);
rl = readline.createInterface(process.stdin, {});
rl.on('line', function(data) { console.log('line: ' + data); });
5) My own variant. Use another module 'split' - it allows to read from stream and devide data into chuks by specified symbol (\r?\n by default). I used it to work with socket and as soon as stdin is also readable stream - we can use it here.
var split = require('split');
process.stdin.setEncoding('utf8');
process.stdin.pipe(split()).on('data', function(data) { console.log('line: ' + data); });
My question is "What is process.openStdin();????"
I've searched every page in google, but didn't found any documentation on this function!
Also while searching I've discovered, that official documentation for nodejs is ugly - not mentioned since which version methods are available, no detailed description on many objects/methods, no user comments. And this method (openStdin) - exists and works, but nowhere discribed! WTF???

Answer 1

While writing the question I've found the answer :)
It is in source code of nodejs:
process.openStdin = function() {
process.stdin.resume();
return process.stdin;
};
But I wonder, why is it not described in documentation? If it is a function for private use only, why is it used by many people, who wrote about working with stdin?