R NAMESPACE文件中的export和S3方法

Question

以下是R包中NAMESPACE文件中的一些行

S3method(diseq,table)
S3method(diseq,genotype)
S3method(print,diseq)
S3method(print,genotype)
S3method('==',genotype)
S3method('==',haplotype)
S3method('%in%',default)
S3method('%in%',genotype)
S3method('%in%',haplotype)
S3method('[',genotype)
S3method('[',haplotype)
S3method('[<-',genotype)
S3method('[<-',haplotype)
S3method(heterozygote,genotype)
S3method(homozygote,genotype)
#S3method(print,allele.count)
S3method(print,allele.genotype)
#S3method(allele.count,genotype)
#S3method(allele,genotype)
S3method(print,LD)
S3method(print,LD.data.frame)
S3method(print,summary.LD.data.frame)
S3method(plot,LD.data.frame)
S3method(print,summary.genotype)
S3method(plot,genotype)
S3method(order, default)
S3method(order, genotype)
S3method(sort, genotype)

importFrom(stats, na.omit)
importFrom(gdata, interleave, trim)
importFrom(mvtnorm, rmvnorm)
##importFrom(combinat, rmultz2) # combinat doesn't have a namesspace.
importFrom(gtools, binsearch, combinations, permutations)

export和S3method有什么区别？他们做了什么？

我注意到LD已导出并注册S3method，为什么这是必要的？