The WCAG 2.0 brings with it many recommendations which are not only necessary for accessibility but much overdue when it comes to SEO. Most people don't realize that search engines are actually blind. As such, they can't see photos, can't conceptualize page layouts, can't see colour indicators... oh and did I mention they were deaf too?
On this page I will be covering WCAG 2.0 as it applies to...
Links to PDF files
The Government of Canada CLF 2.0 traditional approach was to creating PDF links has been Report Summary - 2011 Edition (PDF, 365 KB) where the first link is to the HTML page and the second is to the PDF version. However with the introduction of WCAG 2.0 which recognizes that PDF files can now be an accessible format all on their own, an HTML version of a PDF file is no longer required as long as the PDF is WCAG 2.0 Level AA compliant.
Guidelines like the CLF 2.0 recommend formatting links to PDF files like Report Summary - 2011 Edition (PDF 3.7 MB) when only a PDF file is available. When it comes to accessibility, this is actually incorrect for the following reasons:
- The CLF recommended format is non-compliant with Success Criterion 2.4.4 (Link Purpose (In Context)). It would be no different than having a "Click here to view the publication." type link.
- Our format lets folks using a screen reader know that this links to a PDF file and not to an HTML page as they are tabbing through the links. Otherwise there is an assumption that links will lead to an HTML page. By leaving the PDF out of the link, there is no clear indication in the link alone that it will lead to a PDF file unless the user takes the time to also listen to the context surrounding the link. In fact, if you had a series of PDF only publications, the user would just hear "PDF, PDF, PDF, PDF..." as they tabbed through the links on the page which would be meaningless to someone using a screen or braille reader.
- Search engines place higher value on text within a link. In fact, the link in Report Summary - 2011 Edition - (PDF 3.7 MB) is meaningless to a search engine and provides no SEO value at all. In fact may actually count against you if there many links called PDF on the page. In effect, you are creating an accessibility issue which did not exist when the text was linked to the HTML version.
In the spirit of best practices, as long as your PDF file is accessible, we recommend you use one of the following formats when creating a link to a PDF file.
- If both an HTML and a PDF version of the content exist:
Report Summary - 2011 Edition (PDF 3.7 MB)
- If only a PDF version (no HTML page) exists:
Report Summary - 2011 Edition - PDF (3.7 MB)
Just listen to these links from a screen reader's perspective and you will quickly realize that it makes so much more sense.
Formatting File Sizes
The following guidelines should be used when specifying file sizes for file downloads (PDF, videos, etc).
For size in English, use (in uppercase):
- 1-999 KB
- 1.0+ MB
For size in French, use (in lower case):
- 1 à 999 ko
- 1,0 et plus mo
If you are using abbreviations for units of size such as kilobytes (KB) and megabytes (MB) as in the previous examples, remember that these will need to be wrapped in a set of abbreviation (abbr) tags.
Good catch Lydia! Thank you for pointing out this often overlooked point. KB, MB, ko and mo are all abbreviations and should be wrapped in an appropriate abbr tag.