For WDL questions, see the WDL specification and WDL docs.
For Cromwell questions, see the Cromwell docs and please post any issues on Github.
alternative command execution based on input parameters?
Do you have an example of a WDL workflow that accepts alternative input parameters, and based on the inputs will execute the workflow accordingly? For example, having a WDL that accepts either bam or fastq files as input. If the bam file is selected, then it will process a different set of initial tasks than if the fastq file was provided.