Page markup keeps ampersands, angle brackets and HTML entities
Page and blog-post markup sent on create and update now keeps every & and < you write, in text and in attribute values. "Tom & Jerry", "R&D", &, ©, and a link like href="https://example.com/?utm_source=a&utm_medium=b" all land on the page as written. Before this, a bare & or an HTML named entity was silently dropped, and every UTM link lost its parameters.
Markup read back with expand[]=markup now escapes & and <, so you can send what you read straight back without losing characters on the second write.
Agent examples: an agent can write a company name like "AT&T" or a tracked campaign link into a page and trust it renders exactly that, and can read a page, change one headline and send the whole markup back safely.
Resources: Page · Page markup guide