WCAG guidelines are categorized into 3 levels of conformance, each is progressively harder – A (lowest), AA (mid-range), AAA (highest). 较高级别的一致性确保了较低级别的自动一致性. A级设置了最低的可访问性标准，不包括更广泛的可访问性. A级是AA级的一个子集，你必须满足25个标准才能达到A级. Level AA requires a bit more commitment. 要达到AA级，除了满足A级的25项标准外，还需要满足13项标准. However, it is recommended to go for AA conformance for all websites.