Syntax

A template is ordinary text. Anything outside curly braces renders as it was written. Anything inside them is a tag.

The shape of a tag

{declaration(parameter):payload}
{declaration.parameter:payload}

Part	What it is
declaration	The tag name, such as `if`, `random` or `upper`. Always first. Most tags accept several names.
parameter	An option for the tag, in `(...)` or after a `.`. Some tags require one, some ignore it.
payload	The text the tag works on, after a `:`. Some tags require one, some ignore it.

Not every tag uses every part:

{delete}
{upper:hello}
{slice(0-5):Hello World}
{args.2}

Tag names ignore case, so {upper:hi} and {UPPER:hi} do the same thing. Variable names do not, so {user} and {User} are two different variables.

The two parameter forms

(...) and . mean the same thing. The parenthesis form ends at the closing bracket. The dot form ends at the :, or at the end of the tag if there is no payload.

{args(2)}
{args.2}

Use parentheses when the parameter contains a : or a . of its own, since the dot form would end too early.

Nesting

Tags nest, and the inner one renders first. That is how you feed one tag's output into another:

{upper:{lower:ABC}}
# ABC

{if({random:yes,no}==yes):Sure!|Nope.}

Escaping

Put a backslash in front of a character to stop it being read as syntax. That works for {, }, (, ), : and |.

Use \{braces\} to write a tag.

The backslash stays in the rendered output. If you need clean text, remove the backslashes on your side after the render, or avoid the character.

The escape tag does this to a whole piece of text at once, which is the safer option when you are dropping one value into another tag.

Several tags split their payload on |. if uses it to separate the true branch from the false one, any and all use it between expressions, and embed(field) uses it between the name, value and inline flag.

{if(1<2):true branch|false branch}

Only the first | splits if. Everything after it, pipes included, is the false branch, which is what lets you nest a second if in there.

What happens to a tag nobody handles

It stays exactly as you wrote it:

Hi {nobodyImplementedThis}
# Hi {nobodyImplementedThis}

So if a tag shows up in the output instead of doing something, one of three things is true: the name is misspelled, the app did not register that tag, or the tag needed a parameter or a payload you did not give it.

Limits

The app running your template can cap how much output it produces. Go over the cap and the render fails rather than returning a truncated message. It can also cap how much text is read from inside a single {...}, which defaults to 2000 characters.