Can anyone explain how does the below xsl works? - xslt

Question

Can anyone please exlain how the below xsl works with an example?
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<!-- Remove empty elements or attributes -->
<xsl:template match="#*|node()">
<xsl:if test=". != '' or ./#* != ''">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:if>
</xsl:template>
</xsl:stylesheet>
When i use above xsl for below xml which is not indented (Note it is showing indented below but consider it not indented. The input text box did not allow me to put not indented xml):
<Book Edition="1234" Type="Novel" TimeStamp="2021-07-09T14:02:55-05:00" Version="1.003">
<BOS>
<LIB>
<RequestorID ID="XXX" Type="10"/>
</LIB>
</BOS>
<Sections>
<Section CreateDateTime="2021-07-03T11:21:43-05:00" CreatorID="XXX" Status="Read">
<UniqueID ID="443791" Type="10"/>
<Chapters>
<Chapter>
<Paragraphs>
<Paragraph NumberOfUnits="10" Lines="100">
<Rates>
<Rate EffectiveDate="2021-12-12" ExpireDate="2021-12-13" RateTimeUnit="Day" UnitMultiplier="1">
<Base AmountBeforeTax="145.90" CurrencyCode="USD"/>
</Rate>
</Rates>
</Paragraph>
</Paragraphs>
<Readers>
<Reader Age="10" Count="1"/>
</Readers>
<TimeSpan End="2021-12-13" Start="2021-12-12"/>
<BasicInfo BookCode="1310"/>
</Chapter>
</Chapters>
<Authors>
<Author AuthorRPH="1">
<Profiles>
<ProfileInfo>
<UniqueID ID="44379" Type="1"/>
<Profile ProfileType="1">
<Author>
<PersonName>
<GivenName>TEST</GivenName>
<Surname>TEST</Surname>
</PersonName>
<Telephone PhoneNumber="0"/>
<Email>test#test.com</Email>
<Address Type="H">
<AddressLine>123 MAIN ST</AddressLine>
</Address>
</Author>
</Profile>
</ProfileInfo>
</Profiles>
</Author>
</Authors>
<GlobalInfo>
<ReadIds>
<ReadId ReadID_Source="ZZZ" ReadID_Type="10" ReadID_Value="1234"/>
</ReadIds>
</GlobalInfo>
</Section>
</Sections>
</Book>
Then i get below output:
<Book Edition="1234" Type="Novel" TimeStamp="2021-07-09T14:02:55-05:00" Version="1.003">
<BOS>
<LIB>
<RequestorID ID="XXX" Type="10"/>
</LIB>
</BOS>
<Sections>
<Section CreateDateTime="2021-07-03T11:21:43-05:00" CreatorID="XXX" Status="Read">
<UniqueID ID="443791" Type="10"/>
<Authors>
<Author AuthorRPH="1">
<Profiles>
<ProfileInfo>
<UniqueID ID="44379" Type="1"/>
<Profile ProfileType="1">
<Author>
<PersonName>
<GivenName>TEST</GivenName>
<Surname>TEST</Surname>
</PersonName>
<Telephone PhoneNumber="0"/>
<Email>test#test.com</Email>
<Address Type="H">
<AddressLine>123 MAIN ST</AddressLine>
</Address>
</Author>
</Profile>
</ProfileInfo>
</Profiles>
</Author>
</Authors>
</Section>
</Sections>
</Book>
As seen above it removes everything inside the Chapters tag and Global info tag
But if i use above xsl for below xml which indented:
<Book Edition="1234" Type="Novel" TimeStamp="2021-07-09T14:02:55-05:00" Version="1.003">
<POS>
<Source>
<RequestorID ID="XXX" Type="10"/>
</Source>
</POS>
<Sections>
<Section CreateDateTime="2021-07-03T11:21:43-05:00" CreatorID="XXX" Status="Read">
<UniqueID ID="443791" Type="10"/>
<Chapters>
<Chapter>
<Paragraphs>
<Paragraph NumberOfUnits="10" Lines="100">
<Rates>
<Rate EffectiveDate="2021-12-12" ExpireDate="2021-12-13" RateTimeUnit="Day" UnitMultiplier="1">
<Base AmountBeforeTax="145.90" CurrencyCode="USD"/>
</Rate>
</Rates>
</Paragraph>
</Paragraphs>
<Readers>
<Reader Age="10" Count="1"/>
</Readers>
<TimeSpan End="2021-12-13" Start="2021-12-12"/>
<BasicInfo BookCode="1310"/>
</Chapter>
</Chapters>
<Authors>
<Author AuthorRPH="1">
<Profiles>
<ProfileInfo>
<UniqueID ID="44379" Type="1"/>
<Profile ProfileType="1">
<Author>
<PersonName>
<GivenName>TEST</GivenName>
<Surname>TEST</Surname>
</PersonName>
<Telephone PhoneNumber="0"/>
<Email>test#test.com</Email>
<Address Type="H">
<AddressLine>123 MAIN ST</AddressLine>
</Address>
</Author>
</Profile>
</ProfileInfo>
</Profiles>
</Author>
</Authors>
<GlobalInfo>
<ReadIds>
<ReadId ReadID_Source="ZZZ" ReadID_Type="10" ReadID_Value="1234"/>
</ReadIds>
</GlobalInfo>
</Section>
</Sections>
</Book>
Then i get correct output:
<Book Edition="1234" Type="Novel" TimeStamp="2021-07-09T14:02:55-05:00" Version="1.003">
<BOS>
<LIB>
<RequestorID ID="XXX" Type="10"/>
</LIB>
</BOS>
<Sections>
<Section CreateDateTime="2021-07-03T11:21:43-05:00" CreatorID="XXX" Status="Read">
<UniqueID ID="443791" Type="10"/>
<Chapters>
<Chapter>
<Paragraphs>
<Paragraph NumberOfUnits="10" Lines="100">
<Rates>
<Rate EffectiveDate="2021-12-12" ExpireDate="2021-12-13" RateTimeUnit="Day" UnitMultiplier="1">
<Base AmountBeforeTax="145.90" CurrencyCode="USD"/>
</Rate>
</Rates>
</Paragraph>
</Paragraphs>
<Readers>
<Reader Age="10" Count="1"/>
</Readers>
<TimeSpan End="2021-12-13" Start="2021-12-12"/>
<BasicInfo BookCode="1310"/>
</Chapter>
</Chapters>
<Authors>
<Author AuthorRPH="1">
<Profiles>
<ProfileInfo>
<UniqueID ID="44379" Type="1"/>
<Profile ProfileType="1">
<Author>
<PersonName>
<GivenName>TEST</GivenName>
<Surname>TEST</Surname>
</PersonName>
<Telephone PhoneNumber="0"/>
<Email>test#test.com</Email>
<Address Type="H">
<AddressLine>123 MAIN ST</AddressLine>
</Address>
</Author>
</Profile>
</ProfileInfo>
</Profiles>
</Author>
</Authors>
<GlobalInfo>
<ReadIds>
<ReadId ReadID_Source="ZZZ" ReadID_Type="10"
ReadID_Value="1234"/>
</ReadIds>
</GlobalInfo>
</Section>
</Sections>
</Book>
Can anyone explain if the xmls are same why does indentation give different output? Does proper indentation affect the xsl transformaion?

Answer 1

The code has a single template rule which matches all element, text, comment, processing instruction, and attribute nodes. If the node has a non-empty string value, or has an attribute with a non-empty string value, then it shallow-copies the node and processes its attributes and children recursively.
The overall effect is to copy the entire document except for elements that have no content and no non-empty attributes (such as <br/>) - plus a few other exceptions such as empty comments.

Answer 2

The XPath expression . != '' or ./#* != '' in the test might not behave as you expect. The specification for XPath 1.0 (usually used with XSLT 1.0), as indicated by version="1.0" says at https://www.w3.org/TR/1999/REC-xpath-19991116/#dt-string-value
For every type of node, there is a way of determining a string-value
for a node of that type. For some types of node, the string-value is
part of the node; for other types of node, the string-value is
computed from the string-value of descendant nodes.
and down in section "5.2 Element Nodes"
The string-value of an element node is the concatenation of the
string-values of all text node descendants of the element node
in document order.
So for an ordinary non-indented source element, string conversion involves recursively descending to elements and getting their values (ignoring attributes). In your case, for an element which also does not have attributes, the whole sub-tree gets eliminated (i.e. not copied to output) if it does not have any element with a value like <elem>value</elem> in it.
With indented source, you also have nodes representing the whitespace between the nodes. (XPath does not know that white-space is irrelevant for you, and assumes mixed content.) This causes to-string conversion of an element with (indented) sub-elements to have (at least) that whitespace in the result of the string conversion, rendering the . != '' XPath expression false.
I hope, this explains the difference in result depending on indentation in source.
You might want to have a look at https://www.w3.org/TR/1999/REC-xpath-19991116/#function-normalize-space for trimming the conversion result. Note that this would potentially also affect honoring of "real values" if these can be all whitespace.
Edit: Depending on what you want to achieve, you might consider having white-space eliminated by the XSLT processor by using xsl:strip-space.