单词head-margin
网络: 天头；头白边；版口
Margins: White space around the image area of a page. They are back margin, head margin, for edge margin and foot margin respectively.
白边：页内围绕印纹面积的空白位。分别为内白边，头白边，外白边和脚白边。
Head margin: The margin at the top of a page.
头白边：书页上边的空白部份。
For example, the head margin in this template measures proportionately more than is customary.
例如，在模板的比例超过惯例的措施。
Air Flow and Head Margin of Boiler Primary Fans with Their Reasonable Matching and Number Selection
锅炉一次风机风量、压头裕量及其合理匹配和台数的选择
Development of Automatic Test Experiment Set for Head Margin Stress
封头边缘应力自动测试实验装置的研制