Update 2/3/17:

I tested linking a ticketed event to a donation page that only accepts a single amount, and the process worked as expected. I have moved your suggestion to the questions area of our website, as your request is to clarify documentation rather than to suggest a change to the product. 

The donation page does not need to accept multiple amounts nor do you need to leave the default donation levels in place to use the page to pay for event tickets. As others have noted, when a supporter is passed from an event RSVP page to a donation page or an invoice page to pay for the transaction, the amount to be paid is passed to the payment page using a cookie.

There are a couple of things to note:

Some customers have requested that the ticket payment process should be redesigned so that cookies do not need to be enabled to complete the transaction. 

An FAQ was written on how to customize a donation page to let potential attendees know they need to enable cookies in order to finalize ticket purchase. 

We recommend creating a separate donation page for each ticketed event. Doing this ensures that money received for a specific event can be tracked separately and will not be commingled with money received as part of a general appeal.

Donations made through a specific page can automatically place a person on a path and assign a control panel person responsibility for the path or path step. Part of their responsibility can be to confirm a one-to-one relationship between donations received and RSVPs listed within the event, to ensure that ticket payments are not separated from event RSVPs. 

The reason a donation page attached to a ticketed event should have 'accept multiple amounts' checked is to allow people to pay for tickets even if they have disabled cookies in their browser. This is a work-around. We expect most site visitors will have cookies enabled and will have a seamless process paying for ticketed events.

It is also true that if the social share prompt is enabled on the donation page where event tickets are purchased, supporters who click through Twitter or Facebook to that page would complete a transaction without RSVPing for the event. In this case, it is important to decide whether to continue using the social share prompt on the page and what options you want to appear on the donation page if it is opened without clicking through the event page.

In the course of reviewing your request, I found several problems with our create a donation page HOWTO that I am addressing. Of particular relevance is the need to acknowledge that we recommend creating a separate donation page for each ticketed event that is not included in the top nav or other site navigation. 

1/27/17: 

Thanks! Do you mean in our documentation or in the control panel itself? Or, maybe both?