\ban(?=d\b)

将匹配和中的an，但不是an，hand等。

will match "an" in "and", but not in "an", "hand", etc.

(?<=\bsimp)lg\b

将匹配simplg中的lg，但不会匹配lg，bulge等等。



正则表达式语言 - 快速参考 [ ^ ]

Expresso正则表达式工具 [ ^ ]

will match "lg" in "simplg", but not in "lg", "bulge", etc.

Regular Expression Language - Quick Reference[^]
Expresso Regular Expression Tool[^]

不是解决方案，但链接可能有用。

以下是RegEx文档的链接：

perlre - perldoc.perl.org [ ^ ]

以下是工具的链接帮助构建RegEx并调试它们：

.NET正则表达式测试程序 - 正则表达式风暴 [ ^ ]

快速正则表达式工具 [ ^ ]

这个显示RegEx是一个很好的图表，它非常有助于理解RegEx的作用：

Debuggex：在线可视正则表达式测试器。 JavaScript，Python和PCRE。 [ ^ ]

Not a solution, but links may be useful.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[^]
Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[^]
Expresso Regular Expression Tool[^]
This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx:
Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[^]