PlaceholderElement
PlaceholderElements can be used to represent elements in code matchers templates and code templates. They represent variable elements in ASTs.
Code matchers recognize portions of ASTs, while code templates generates portions of ATS. For example, in a code matcher we could use a PlaceholderElement to indicate that a certain part of an AST could vary and that we want to recognize that value. We could have an AST of this type: SumExpr(PlaceholderElement("left"), IntLiteral(1)). A code matcher could recognize all of these expressions as matching: SumExpr(IntLiteral(2), IntLiteral(1)), SumExpr(ReferenceExpression("foo"), IntLiteral(1)), or SumExpr(MultiplicationExpr(IntLiteral(2), IntLiteral(3)), IntLiteral(1)). What would vary among these cases would be the value recognized for the PlaceholderElement.
Conversely, in a code template the PlaceholderElement indicates where to insert parameters provided to populate the template.
Functions
Return true if the node can be represented by this PlaceholderElement. For example, a certain PlaceholderElement could be used only to match expressions or statements. In case this is a multiple quoted element, and it is used to match many elements, each element should be passed to this method. For example, if a certain PlaceholderElement is used to match a sequence of three statements S1, S2, and S3, all of them should be passed, one by one, as parameters of this method.