Just try this:
\bYour_Keyword_to_find\b
\b
is used in RegEx for matching word boundary.
[EDIT]
You might be looking for this:
(?<=<span>)([^<>]+?)(?=</span>)
Explanation:
<!--
(?<=<span>)([^<>]+?)(?=</span>)
Options: case insensitive; ^ and $ match at line breaks
Assert that the regex below can be matched, with the match ending at this position (positive lookbehind) «(?<=<span>)»
Match the characters “<span>” literally «<span>»
Match the regular expression below and capture its match into backreference number 1 «([^<>]+?)»
Match a single character NOT present in the list “<>” «[^<>]+?»
Between one and unlimited times, as few times as possible, expanding as needed (lazy) «+?»
Assert that the regex below can be matched, starting at this position (positive lookahead) «(?=</span>)»
Match the characters “</span>” literally «</span>»
-->
[/EDIT]