Paising HTML

I've recently been brushing up my Maths by reading old text books. A great obstacle to understanding is the need to follow references of the form:

'see example 4 following theorem 2 in section 9'

Usually such references contain no page numbers, and section numbers are shown only on the first page of each section, not at the heads of individual pages. I need a bookmark to keep my place, and even then by the time I've shuffled through numerous pages to locate the reference I've often forgotten why I needed it.

In an html document one simply clicks on the reference, and there is it. The BACK key returns on to the original. There are many reasons for publishing online, but the ease of cross referencing is rarely mentioned.