{true} answers TRUE - the plain hit of a level. Written as a pair, its content renders exactly once and there is no data to iterate; written alone it prints nothing. It is the fixed "yes" of the three constant tags, beside {false} and {null}.

Its use is as a neutral level to hang options on. Every tag takes the generic options, so {true tidy}...{/true} tidies a stretch of HTML, {true toContent='box'} keeps its rendered content in a store, and {true $total = 0}...{/true} gives a block a variable of its own that is unwound when the block closes. In tests it switches a branch on without changing anything else.

Because it is a hit, an @else@ part of a {true} never renders.