A heavily inflexible and hard to understand syntax within TYPO3 is the so-called "typolink" syntax. The first parameter here decides where to link to - a page, a file, an external link or an email address. This syntax was extended over the years and the several changes, also with the introduction of FAL, made it quite difficult to move forward in a lot of areas, especially when it comes to implementing a new Rich Text Editor (RTE).
The new linking syntax sets some proper defaults by prefixing "t3://page" when linking to a page within the TYPO3 instance, and "t3://file" for files. The old syntax, which is still used in all places of the TYPO3 Core, and in existing installations can still be used without any drawbacks. The infrastructure under the hood however is streamlined so further work on the linking logic can continue. The next step will be to remove the <link 123> tag which TYPO3 stored in the database in RTE fields, and replace it with a regular <a href="t3://page?uid=123"> tag inside the database. This also removes a lot of RTE parsing when editing or saving content and opens the door for simpler integration of Frontend Editing.