Use when creating a new custom field on any Salesforce object: choosing field type, setting API name, configuring Field-Level Security, adding to page layouts, and deploying. Triggers: 'add a field', 'new custom field', 'what field type should I use', 'FLS not working', 'field not showing on page layout'. NOT for creating the object itself - use admin/object-creation-and-design. NOT for formula field logic - use admin/formula-fields. NOT for picklist value set management - use admin/picklist-and-value-sets. Also covers: field-meta.xml, CustomField metadata, deleteConstraint, externalId, unique, precision and scale, relationshipOrder, writeRequiresMasterRead, fieldPermissions, package.xml for fields.
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