We're declaring that subview's left margin should align to superview's left margin.

我们声明子视图的左边缘应该对准上海华的左边缘。

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In this format each typed element - except the date and the signature block - begins at the left-hand margin. The date may be backspaced from the right margin point to align at the right margin;

这种格式下，书信的排版，除了日期和签名部分，都从左边空白处开始，没有空格，段段之间空行。

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