Required. Controls over how job documents get ranked on top of
existing relevance score (determined by API algorithm). A
combination of the ranking expression and relevance score is
used to determine job's final ranking position. The syntax
for this expression is a subset of Google SQL syntax.
Supported operators are: +, -, *, /, where the left and right
side of the operator is either a numeric [Job.custom_attribut
es][google.cloud.talent.v4beta1.Job.custom_attributes] key,
integer/double value or an expression that can be evaluated to
a number. Parenthesis are supported to adjust calculation
precedence. The expression must be < 100 characters in length.
The expression is considered invalid for a job if the
expression references custom attributes that are not populated
on the job or if the expression results in a divide by zero.
If an expression is invalid for a job, that job is demoted to
the end of the results. Sample ranking expression (year + 25)
* 0.25 - (freshness / 0.5)
