What kind of websites can I bookmark?
Articles is intended for bookmarking text based content. This means you can save almost any news or blog article for reading later.
It will however not work if you try to bookmark e.g. a site's home page, search results, videos, image galleries, tweets or other non textual pages. In this case, the content can not be determined.
Can I bookmark protected articles?
In contrast to other read it later apps, Articles allows to also save password or paywall protected pages.
This is however only possible when bookmarking from Safari or integrated in-app browsers, as in this case the page is directly stored on your local device. If you bookmark a shared link, a protected url can not always be successfully resolved.
Why can the content of some articles not be determined?
While many articles can be successfully extracted, the content of some pages can not be determined.
In most such cases, there is simply not enough text available to determine what the actual content is. If you for example try to bookmark a Twitter post, the 280 characters do not represent the main content of the overall page.
Another case where article extraction can fail are websites with outdated, non-standard or unstructured formats. For pages without semantic markup, it is simply not possible to determine what the actual content is. If text is contained in div or span elements instead of paragraphs, a parser can not know its meaning in context of an article.
Why are some article images not loaded?
When saving an article, text as well as images are processed and converted to a minimal format.
Like with text paragraphs, images need to be formatted according to official standards as well. In case a website uses non-standard or unstructured formats, such non-semantic images can not be loaded.
Many websites also use so called "lazy loading" images, which are only downloaded when scrolled into view. Articles supports such images as well, but only if they are implemented according to certain standards. If a website uses some other custom made image loading, it is not possible to determine an image's source.