Glossary
Fluid
The template language of TYPO3. It decides how data is turned into HTML.
What Fluid does
Fluid turns data into HTML. It receives variables, a record or a list for instance, and outputs markup. The syntax uses curly braces for variables and tags of its own for everything else.
The principle is deliberately plain. A template should stay readable, including for somebody who does not write PHP.
ViewHelpers
Where plain output is not enough, ViewHelpers come in. They are small, reusable building blocks for jobs such as creating links, processing images, formatting numbers or shortening text.
TYPO3 ships with a great many of them. Writing your own makes sense when a particular piece of presentation logic keeps recurring in a project. They are the right home for anything that would otherwise end up as an impenetrable nest in the template.
Working with TypoScript
Fluid and TypoScript share the work. TypoScript decides which template is responsible for which case and what data is handed in. Fluid decides how that data is presented.
When something goes wrong, that split is the first useful diagnosis. If a variable is missing in the template, the cause usually sits in TypoScript or in the controller, not in the template itself.
In the sitepackage
The Fluid files of a project live in the sitepackage, separated into templates, layouts and partials. That structure is a convention, and it is worth keeping even on small projects, because it does not have to be rebuilt as things grow.