We’re telling it that we don’t want to see any notices or warnings, but rather just errors. If you want to do a more comprehensive check, you can show the warnings too, by omitting it from the command.
Out of the box, pa11y supports 4 accessibility standards: Section508, WCAG2A, WCAG2AA, WCAG2AAA. The default is WCAG2AA, but you can specify any standard you want via the –standard command line argument.
All of the WCAG2* standards are the same international standard, but with different levels of strictness (A being the least strict, AAA being the most strict). Additional information on WCAG levels can be found in Understanding Levels of Conformance.
The Section508 standard is for US Federal & State government institutions, should you be working on websites for them.
But we’re just going to use the default WCAG2AA standard, which is middle of the road in terms of strictness (and indeed is the standard that WCAG suggests to use), and is used by default if we don’t specify a –standard.
Here’s what the output looks like: