where variable is a freely chosen name and expr is a template expression.
Note that we use the "beaver operator" := for assignments. A simple = is the "equal operator". Additionally, there may be no whitespace between the {{, the $ and the name of the variable.
The name of the variable must begin with a letter or underscore, followed by an arbitrary sequence of letters, numbers and underscores.
The visibility of the variable is limited to the current template. Global variables (e.g. $env) may be overridden locally in a template without affecting its global value.
Local variables can hold strings, numbers, booleans, JSON Objects and arrays or DOM node-sets. Variables can be reassigned.
