From the Knowledge Manager Manual:
none: Disables field extraction for the source, source type, or host
identified by the stanza name. You can use this setting to ensure that
other regexes that you have created are not overridden by automatic
field/value extraction for a particular source, source type, or host. You can
also use this setting to increase search performance by disabling
extraction for common but nonessential fields. We have some field
extraction examples at the end of this topic that demonstrate the disabling
of field extraction in different circumstances.
json: Use this setting if you intend to use the field extraction stanza to
extract fields from JSON data.
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