这听起来像你无所适从多行的意思。单行注释源头code的行末结束，如果你想继续这样评论，你必须把/// 下一行。多行注释以a开头 / * ，并着有 * / ，所以它可以结束结束无论是在同一行或多个行向下

作为多行只字未提任何如何在注释中的文本显示。为了把一个换行符在XML注释必须插入＆LT; BR /＆GT; （破发），或者换行的＆LT ;第方式＆gt; （段落）标签

According to this article, it's possible to get multiline XML comments -- instead of using ///, use /** */. This is my interpretation of what multiline comments are, and what I want to have happen:

/**
 * <summary>
 * this comment is on line 1 in the tooltip
 * this comment is on line 2 in the tooltip
 * </summary>
 */

However, when I use this form, the tooltip that pops up when I hover over my class name in my code is single-line, i.e. it looks exactly as if I had written my comment like this:

/// <summary>
/// this comment is on line 1 in the tooltip
/// this comment is on line 2 in the tooltip
/// </summary>

Is this behavior actually possible still in VS2008?

EDIT

gabe pointed out that I have misunderstood what "multiline" means, and I actually need to use <para> or <br> to get my intended effect. I went ahead and used <br> because I want to control where the line breaks occur, i.e.

/// <summary>
/// this comment is on line 1 in the tooltip<br/>
/// this comment is on line 2 in the tooltip<br/>
/// </summary>

When I look at the tooltip for this class in my code, everything still ends up on one line... WTH? Did I do something wrong here?

UPDATE

Ok, I went ahead and tried the <para> tag on each line, and that works. Not sure why <br/> doesn't.

/// <summary>
/// <para>this comment is on line 1 in the tooltip</para>
/// <para>this comment is on line 2 in the tooltip</para>
/// </summary>

It sounds like you are confused about what "multi-line" means. A single-line comment ends at the end of the line of source code, and if you want to continue that comment you must put a "///" on the next line. A multi-line comment starts with a "/*" and ends with a "*/" so it can end either on the same line or multiple lines down.

Being "multi-line" says nothing about any how the text within the comment is displayed. To put a line break in an XML comment you must insert a <br/> ("break") or wrap the line in a <para> ("paragraph") tag.