Okay I found it, though it is quite complicated logic: https://github.com/ampproject/amphtml/blob/34b74935bdb0da9f39a01c018235f07ceacf4e27/src/base-element.js#

Okay I found it, though it is quite complicated logic: https://github.com/ampproject/amphtml/blob/34b74935bdb0da9f39a01c018235f07ceacf4e27/src/base-element.js#L17 https://github.com/ampproject/amphtml/blob/34b74935bdb0da9f3... also https://github.com/ampproject/amphtml/blob/34b74935bdb0da9f39a01c018235f07ceacf4e27/src/service/resources-impl.js#L1288 https://github.com/ampproject/amphtml/blob/34b74935bdb0da9f3...