Merging values from 2 YAML files in bash

A bash command: $(System.DefaultWorkingDirectory)/yq_linux_amd64 '. *= load("${{ parameters.HELM_CHART_PATH }}/values/DEV/${{ parameters.COMPONENT }}.yaml")' ${{ parameters.HELM_CHART_PATH }}/values/global-values.yaml > $(System.DefaultWorkingDirectory)/deployment-values.yaml Is merging values from 2 YAML files and sending merged output to a single file. I am unable to understand the syntax from the first single quote until the output is redirected. Can anyone help me understand what it means? Why are both operands after the operator, which is *=? . is the current directory, but what does it mean before *=? Also, why only 1st operand is between load () and what is its meaning?