in BuildTasks/Common/Common.ts [487:495]
function getExtensionManifestPaths(): string[] {
// Search for extension manifests given the rootFolder and patternManifest inputs
const rootFolder = tl.getInput("rootFolder", false) || tl.getInput("System.DefaultWorkingDirectory");
const manifestsPatterns = tl.getDelimitedInput("patternManifest", "\n", false) || ["vss-extension.json"];
tl.debug(`Searching for extension manifests: ${manifestsPatterns.join(", ")}`);
return tl.findMatch(rootFolder, manifestsPatterns);
}