QGIS/resources/function_help/json/attribute

{
  "name": "attribute",
  "type": "function",
  "groups": ["Record and Attributes"],
  "description": "Returns an attribute from a feature.",
  "variants": [
    { "variant": "Variant 1",
        "variant_description": "Returns the value of an attribute from the current feature.",
        "arguments": [ {"arg":"attribute_name","description":"name of attribute to be returned"}],
        "examples": [ { "expression":"attribute( 'name' )", "returns":"value stored in 'name' attribute for the current feature"}] },
    { "variant": "Variant 2",
        "variant_description": "Allows the target feature and attribute name to be specified.",
        "arguments": [ {"arg":"feature","description":"a feature"},
                       {"arg":"attribute_name","description":"name of attribute to be returned"}],
        "examples": [ { "expression":"attribute( @atlas_feature, 'name' )", "returns":"value stored in 'name' attribute for the current atlas feature"}] }
   ]
}