Skip elements do not exist for more fast scraping.
In some pages (amazon..other) to obtain all the content it is necessary to add selectors that are not in all the pages...
For example, for images, click and get link for each one, but if there isn't more, no need to process the remaining selectors...
Is posible this it's the best example...
li:nth-of-type(1)
li:nth-of-type(2)
li:nth-of-type(3)
li:nth-of-type(...)
li:nth-of-type(15)
and the rest selectors.
So if in the (3) no exist, no continue, skip the rest selectors.
It would be something like if element count is 0 it doesn't load the rest of the elements.
So you can make an sequence of selectors for permanent fields and another for variable fields.