Better YML validation when configuration uses YML anchors and references

As per the title, the YML validator for Pipelines (https://bitbucket-pipelines.prod.public.atl-paas.net/validator) does not show any syntax errors for yml anchors.

This is highlighted in this example public repository: https://bitbucket.org/rtest123/anchor-indentation/addon/pipelines/home#!

Added by tboudale :

I would also like to add that sometimes a YML anchor also breaks validation in other parts of the yml file.

E.g.

definitions: 
  steps:
    - step: &build-test
      name: Build and test
      script:
        - echo "hello"
      artifacts:
        - target/**

pipelines:
  branches:
    anchor:
      -step: *build-test
    master:
      - step: *build-test

Above^ the lack of a space between '-' and 'step' for the branch named 'anchor', is not indicated by the validator.