[Doitsu]

The Sigil PCRE library already supports conversion to upper case and lower case with \U, \u, \L and \l back references.

For example:

Find: <p>(.*?)</p>
Replace: <p>\U\1\E</p>
Before:

<p>This is a test sentence.</p>

After:

<p>THIS IS A TEST SENTENCE.</p>

Find: <h3>([[:upper:]])([[:upper:]]{2,})
Replace: <h3>\1\L\2
Before:

<h3>CHAPTER 1</h3>

After:

<h3>Chapter 1</h3>

Find: <p>(.*?)</p>
Replace: <p>\u\1</p>
Before:

<p>this is a test sentence.</p>

After:

<p>This is a test sentence</p>

These back references are also useful for Project Gutenberg texts with all caps text instead of italics. For example:

Find: ([[:upper:]]{2,})
Replace: <i>\L\1\E</i>
Before:

<p>This should be in ITALICS.</p>

After:

<p>This should be in <i>italics</i>.</p>