vim帮助文件如何允许可视单词选择以句点选择文本？

我注意到，当我在vim帮助文件中使用命令

viw

时，它能够选择如下字符串：

intro.txt

但是，当我创建一个基本文件并添加文本

intro.txt

并尝试使用

viw

选择整个字符串时，视觉选择会在

处停止，因此我只能选择

intro

，而不选择

.txt

部分

---

有人能解释为什么会这样，以及我如何强制vim选择整个字符串吗？

来自内置帮助：

:help iw

<代码>单词：

A word consists of a sequence of letters, digits and underscores, or a
sequence of other non-blank characters, separated with white space (spaces,
tabs, <EOL>).  This can be changed with the 'iskeyword' option.  An empty line
is also considered to be a word.

---

viW

选择整个单词

A word consists of a sequence of letters, digits and underscores, or a
sequence of other non-blank characters, separated with white space (spaces,
tabs, <EOL>).  This can be changed with the 'iskeyword' option.  An empty line
is also considered to be a word.

'iskeyword' 'isk'   string (Vim default for MS-DOS and Win32:
                        "@,48-57,_,128-167,224-235"
                   otherwise:  "@,48-57,_,192-255"
                Vi default: "@,48-57,_")
            local to buffer
            {not in Vi}
Keywords are used in searching and recognizing with many commands:
"w", "*", "[i", etc.  It is also used for "\k" in a |pattern|.  See
'isfname' for a description of the format of this option.  For C
programs you could use "a-z,A-Z,48-57,_,.,-,>".
For a help file it is set to all non-blank printable characters except
'*', '"' and '|' (so that CTRL-] on a command finds the help for that
command).