Dynamically calculated value, a source file field reference, or a constant can be assigned to a SharePoint column.

A constant can be typed in or a field related to the source file can be selected in the DropDown next to the SP column.
The special fields [Folder01], [Folder02] .. represents the name of the relative folder level to where the file in context is stored.

To dynamically calculate a value, use the expression/rule set, dialog box that relates to each metadata field line. (properties button)
The expression can use the build in functions or it can be a SQL statement for accessing external databases.
All fields related to the individual file in context ([File name], [Size], [Modified] etc. ) plus all system and user defined Parameters can be referenced in the expression.

The predefined set of rules can be used without coding. If specified then the expression is evaluated first then the rule set.
Rules include Replace(), SubString(), Left(), Right() etc. and can be chained for building far more advanced data manipulation than possible with a single expression.

Managed Metadata
When the target column is of type Managed Metadata (Taxonomy) you can assign it text values that will be resolved to the correct GUID within the Term Store.
The automatic Term Store resolving also works with text results from dynamic calculations.
Note that you can paste a specific tag from within the Calculation window.

Valid syntax for Managed Metadata Tagging:

My tag label [My tag label] [My parent tag label][My child tag label] [My parent tag label]:[My child tag label] My parent tag label:My child tag label |{GUID value} make sure you include the pipe character.

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