'in a website' or 'on a website'

'in a website' or 'on a website'
 

SCRIPT is a series of instructions for a computer, carried out in a particular order, for example when a link in a website is clicked.
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My teacher formerly told me only ON a website is possible, never IN a website; what justifies IN in the above sentence? Can I use ON without change of meaning?

Either preposition may be used interchangeably. Author's preference is the only justification I can think of.

Thank you~

Do you mean IN a website/ON a website can be used outside this sentence interchangeably?(This would be very astounding; many a student has been penalised for saying/writing IN a website!

Yes, both are valid. Search the internet for 'in a website' and 'on a website'. You'll find that both are used. They can be used interchangeably.

Thank you, Rusty. But do you mean you've heard native Americans say IN a website or do you just find IN a website on the net? If the latter, google, etc. can't be used to show what is correct English.

I've heard and used both 'in a website' and 'on a website'. Which preposition to use very much depends on my thought process at the moment.

If I'm thinking about the graphical display (what I'm looking at), the link is 'on' the page being displayed.

If I'm thinking about the file that contains the link (and all text surrounding it), the link is 'in' that file.

If I'm thinking about the physical location of the website (or its URL/address), the link is 'at' that place.

Thank you~ Any difference between?(if both correct):

-I got this idea from an article in/on Wiki. (Wiki=Wikipedia)
-In/On Wiki, you can find a lot of useful information.

The same guidelines apply. I would say 'on' when my reference is the graphical display. I would use 'in' when referring to the file system.

Thank you~ Since your answers, which are of course excellent, are quite a surprise to me, I hope you don't mind me putting forward those questions over which my teacher has deducted my marks:

-You can befriend many people in Facebook.
-You can play the soundtrack in the computer.

According to your principle, can we use both IN and ON here interchangeably?

I would choose 'on' in both cases.
Both are examples of using a feature of an application in association with the graphical display. Neither is talking about what underlies the applications.

That said, befriending people 'in Facebook' is possible.
However, playing something 'in the computer', is not. We use 'in' the computer only when we're talking about its components (the motherboard, the drives, the processor, etc.). We run/play applications 'on' the computer.

Thank you. An ulcer could be inside the mouth or on the surface of the skin of the mouth; are IN & ON both correct?

-I've got an ulcer (I'm not sure whether that sore thing caused by accidentally biting the mouth is called so) in/on my mouth.

Both 'in' and 'on' are correctly used, to answer your first question.

In the example you gave, 'on' doesn't work. You have an ulcer in(side) your mouth.
We often say, "I bit my cheek." We all know that that means there's a sore inside our mouth. We can also 'bite our tongue'.

Thank you~

As for the ON/IN difference, do you agree with my explanations?:

-In/ON news programmes, we often hear 'President XYZ says he is steadfast in suppressing universal suffrage'; he said in the past, but since it just happened, we could still use says' (inside the programme, so IN; on TV, on radio, so ON; almost no difference in meaning.)

You're right, in this context both are good.