// adding a compiler hook:
xray\set_compiler_hook(function(string $source, string $filename = null) : string {
    if ($filename === null)  {
        // here we intercept source included through eval()
        // do transformations on $source and return the new $source to be included        
    }
    else {
        // here we intercept source included from a *.php file
        // do transformations on $source and return the new $source to be included
    }
});

// removing the compiler hook:
$hook = xray\restore_compiler_hook();