* - {.., '$pull' : {'fpath' : val1, 'fpathN' : valN, ...}}
* $pullAll Batch version of $pull
* - {.., '$pullAll' : {'fpath' : [array of values to remove], ...}}
+ * $rename Rename field operation
+ * - {.., '$rename' : {'oldfname1' : 'newfname1', 'oldfnameN' : 'newfnameN'}}
+ * $unset Unset the specified fields
+ * - { $unset: { 'fpath1' : "", ... } }
+ * $splice Array field splice operator (like a mongodb $splice) implemented as $do operation.
+ * - ${..., $do : {'fpath1' : {$splice : <limit>}}
+ * - ${..., $do : {'fpath1' : {$splice : [<offset>, <limit>]}}
*
* NOTE: Negate operations: $not and $nin not using indexes
* so they can be slow in comparison to other matching operations.
* - {.., '$rename' : {'oldfname1' : 'newfname1', 'oldfnameN' : 'newfnameN'}}
* $unset Unset the specified fields
* - { $unset: { 'fpath1' : "", ... } }
+ * $splice Array field splice operator (like a mongodb $splice) implemented
+ * as $do operation.
+ * - ${..., $do : {'fpath1' : {$splice : <limit>}}
+ * - ${..., $do : {'fpath1' : {$splice : [<offset>, <limit>]}}
+ *
*
* - Collection joins supported in the following form:
* {..., $do : {fpath : {$join : 'collectionname'}} }