setContextFlag(value) {
    var attr = this.attr;
    attr.setContextFlag = value;
  }
The "set-context-flag" property allows a "flag" to be added to the CompilerContext instance
at compile time if the attribute is found on the node. This is helpful
if an attribute uses a pattern and a transformer wants to have a simple
check to see if any Node in the template has an attribute that matched the pattern.

Example:

"set-context-flag": "myCustomFlag"

A Node instance can be checked if it has a flag set as shown below:

if (context.isFlagSet('myCustomFlag')) { ... }