The Mi{dFlpTag.smGdP-HA.0} element is designed to produce either constitutive or conditional protein tagging when inserted into a phase 0 coding intron of an endogenous gene, with the outcome depending on the orientation of the inserted element relative to the direction of transcription of the gene. It contains a protein trap module composed of a splice acceptor site, a 'smGdP-HA' tag (10 copies of the Tag:HA tag inserted in groups into the backbone of the superfolder green fluorescent protein, which has been rendered non-fluorescent by mutation), and a splice donor site. The protein trap module is flanked by two pairs of mutually incompatible FRT sites (FRT and FRT3) that form a 'FLEx-switch' (PMID:12665802); this means that it can be inverted using FLP recombinase and then stably locked in the opposite orientation (FlyBase curator comment: the inverted and stably locked element is referred to as Mi{dFlpTag.smGdP-HA.0.lock} in FlyBase). If Mi{dFlpTag.smGdP-HA.0} is inserted into an endogenous gene with the protein trap module in the same orientation as the direction of gene transcription, the gene is constitutively tagged. If Mi{dFlpTag.smGdP-HA.0} is instead inserted in the opposite orientation to the direction of gene transcription, the gene is conditionally tagged, because it requires the stable inversion of the protein trap module using FLP recombinase to bring it in to the same orientation as the endogenous gene. The inversion of the protein trap module using FLP recombinase also results in the generation of a functional UAS-driven fluorescent reporter (Disc\RFP^{tdTom.UAS.dFlpTag.lock}), by bringing tdTomato coding sequence under the control of UAS regulatory sequences, allowing for GAL4-driven cell labelling. If a GAL4 driver is used to drive the inversion of the protein trap module in a conditional expression line (by driving expression of a UAS-FLP transgene), the resulting tdTomato labelling can be used to verify the source cells that express the tagged gene of interest. Alternatively, the expression of FLP to drive the inversion of the protein trap module can be independent of the GAL4 driver used to drive expression of the generated Disc\RFP^{tdTom.UAS.dFlpTag.lock} reporter (e.g. by using a hs-FLP transgene).