When you browse to a web site the information will be downloaded from the web server where the information is located. This information consists of the actual content in the form of text and images etc., but also of code that tells your browser how the content will be presented and function.
When we write about technology related to accessibility, we mean all the parts needed for your code to be sent to your browser for it to be interpreted correctly (ie, available).
The technique (simplified speaking) depends on two components, the publishing system, and the code as the one who built the site has created.
If your site uses an interface, publishing system or CMS such as EPiServer and Drupal system contains in itself certain functions that are used to generate code. The person who built the site may not always affect the functions or it hampers the possibilities. Therefore, it´s important that the system generates code that is provided. Some publishing systems are poor at generating available code, and even the good ones today may have had flaws in older versions. Thus, it´s important that you have a good CMS or content management.
Even if you are using a publishing system the one who builds the site must have the right skills to be able to program it so that it becomes available. Today, it is usually here the shortcomings. Not always because of ignorance but also because they choose not to availability customize to save time or because the customer has not asked for it.