XSLT Appending incremented value to existing attribute value - xslt

Question

For my input XML, I have written the XSLT , But I cannot make the XSLT to generate the <mynewtag> correctly. Please help.
XML input:
<?xml version="1.0" encoding="UTF-8"?>
<books>
<book.child.1>
<title>charithram</title>
<author>sarika</author>
</book.child.1>
<book.child.2>
<title>doublebell</title>
<author>psudarsanan</author>
</book.child.2>
</books>
Expected Output:
<?xml version="1.0" encoding="UTF-8"?>
<newbooks>
<newbook>
<mynewtag id="book1" />
<title>charithram</title>
<author>sarika</author>
</newbook>
<newbook>
<mynewtag id="book2" />
<title>doublebell</title>
<author>psudarsanan</author>
</newbook>
</newbooks>
XSLT that I tried: [I understand the syntax is incorrect for <mynewtag> ]. But I don't know to fix it to get the desired output.
<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8"
indent="yes" />
<xsl:template match="/">
<newbooks>
<xsl:for-each select="books/child::*">
<newbook>
<mynewtag id="book<xsl:number value='position()' format='1' />" />
<title>
<xsl:value-of select="title" />
</title>
<author>
<xsl:value-of select="author" />
</author>
</newbook>
</xsl:for-each>
</newbooks>
</xsl:template>
</xsl:stylesheet>
Trying in Online XSLT transformer , http://www.freeformatter.com/xsl-transformer.html
I tried assigning the position to a variable, but still I face the same problem of not knowing how to append it with the attribute value book .
<xsl:variable name="cnt">
<xsl:number value='position()' format='1' />
</xsl:variable>
<xsl:value-of select = "$cnt" />
Note: If I remove the <xsl:number value='position()' format='1' /> from XSL, then the syntax is correct, but then I won't be able to generate book1 book2 etc as <mynewtag> attribute values.
Please help.
Added: <mynewtag> is a required element. It is like any other XML element like <title> that is required in output. It is not an element just to hold the attribute id. Sorry if there is a confusion on this.
Adding Solution here, from the answers obtained to summarize:
<mynewtag>
<xsl:attribute name="id">
<xsl:text>book</xsl:text>
<xsl:number value='position()'/>
</xsl:attribute>
</mynewtag>
or shortly:
<mynewtag id="book{position()}" />"
or
<newbook>
<xsl:variable name="cnt">
<xsl:number value='position()' format='1' />
</xsl:variable>
<mynewtag id="book{$cnt}" />
..........
Also the attribute value templates that IanRoberts mentioned.

Answer 1

You can't place a tag inside another tag. Try either:
<mynewtag>
<xsl:attribute name="id">
<xsl:text>book</xsl:text>
<xsl:number value='position()'/>
</xsl:attribute>
</mynewtag>
or shortly:
<mynewtag id="book{position()}" />"
ADDED:
Not directly related to your question, but I believe the id attribute should be applied to the parent <newbook> element, instead of creating an artificial child element to hold it.