VCF is flexible and allows to express virtually any type of variation by listing both the reference haplotype (the REF column) and the alternate haplotypes (the ALT column). This permits redundancy such that the same event can be expressed in multiple ways by including different numbers of reference bases or by combining two adjacent SNPs into one haplotype (Fig. 1g). Users are advised to follow recommended practice whenever possible: one reference base for SNPs and insertions, and one alternate base for deletions. The lowest possible coordinate should be used in cases where the position is ambiguous. When comparing or merging indel variants, the variant haplotypes should be reconstructed and reconciled, such as in the Figure 1g example, although the exact nature of the reconciliation can be arbitrary. For larger, more complex, variants, quoting large sequences becomes impractical, and in these cases the annotations in the INFO column can be used to describe the variant (Fig. 1f). The full VCF specification also includes a set of recommended practices for describing complex variants.