Final answer:
In web design platforms using block-based editing, the 'max_blocks' tag is used to set the maximum number of blocks allowed in a section.
Step-by-step explanation:
The tag that controls the maximum number of blocks in a section is A. max_blocks. This setting restricts the number of content blocks that can be included within a specific section of a website or a template when using a website content management system or a platform providing similar customization options. It's a common feature in web design platforms that utilize block-based editing.