BED格式有多种，分别为bed3（3列信息），bed6(6列信息)和bed12(12列信息)

chrom 染色体名称，可以是 chr3, chrY, chr2_random 或者 scaffold (e.g. scaffold10671)

chromStart 区间的开始位置

chromEnd 区间的结束位置，与chromStart组成1个0-based [a,b) 的区间，坐标从0开始计数，左闭右开区间

name Label to be displayed under the feature

score 得分水平，0~1000

strand 链的方向，“+”,“-”, “.”

thickStart The starting position at which the feature is drawn thickly (for example, the start codon in gene displays).

thickEnd The ending position at which the feature is drawn thickly (for example, the stop codon in gene displays).

itemRgb An RGB value of the form R,G,B (e.g. 255,0,0). If the track line itemRgb attribute is set to “On”, this RBG value will determine the display color of the data contained in this BED line. NOTE: It is recommended that a simple color scheme (eight colors or less) be used with this attribute to avoid overwhelming the color resources of the Genome Browser and your Internet browser.

blockCount The number of blocks (exons) in the BED line.

blockSizes A comma-separated list of the block sizes. The number of items in this list should correspond to blockCount.

blockStarts A comma-separated list of block starts. All of the blockStart positions should be calculated relative to chromStart. The number of items in this list should correspond to blockCount.