QGIS/resources/function_help/json/eval

{
  "name": "eval",
  "type": "function",
  "description": "Evaluates an expression which is passed in a string. Useful to expand dynamic parameters passed as context variables or fields.",
  "arguments": [ {"arg":"expression","description":"an expression string"}],
  "examples": [
    { "expression":"eval('\\'nice\\'')", "returns":"'nice'"},
    { "expression":"eval(@expression_var)", "returns":"[whatever the result of evaluating @expression_var might be…]"}
  ]
}