Alex's Doc Notes

Repo: Red_Hat_3scale_Documentation
Branch: 2893-index-envars
Topic: apicast-envars.adoc in administering-api-gateway/topics
Guide: Administering the API Gateway

Background:
There is a list of APIcast environment variables in [1]. To find the information of a given environment variable, readers need to scroll the page.

Goal:
At the beginning of the section, add an index of APIcast environment variables. You can make use of IDs and xrefs.

References:
[1] https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.5/html/administering_the_api_gateway/apicast_environment_variables