Introduction to iXBRL [Technical Tagging Guidance]

This article is an introduction to the principles of tagging a set of accounts.  We've started with a run through of how to choose tags what to tag and what to leave.  At the end of the article we've added a general description of a taxonomy along with some specific technical concepts that are used when tagging iXBRL.  Where a concept is referred to in the article you'll be able to head straight to the explanation by clicking the link: e.g. dimensions and tuples.

Over time we'll work to make this document simpler to understand based on your feedback so please let us know if there is anything that is difficult to follow.  The best way to learn iXBRL is to look at a pre-tagged example in either Accounts Production (the test company) or Accounts Plus powered by Compac (the LTD format) and work through this article.


NB.  Accounts Production handles 99% of the tagging for you as do accounts produced in Accounts Plus based on the LTD master.  Custom formats in Accounts Plus will need to be tagged and we'd encourage all users of Accounts Plus to become familiar with the concepts explored in this article.


XBRL - Basic principles of data tagging


In the simplest terms the XBRL tagging of a report is achieved by matching a tag in the taxonomy to a data item in a financial statement. The data item concerned may consist of a monetary value an ordinary number a date a section of text or some other standard type of data.


For example if a financial statement contains the line item 'Operating profit £300000' then the value £300000 should carry the XBRL tag whose label is 'Operating profit (loss)'. Note that only financial values carry the monetary tag; the description in the human–readable accounts remains untagged and is handled purely as text.


Some textual data in reports has associated tags and should be tagged accordingly. This includes the text of specific declarations policies and descriptions.

Data which applies to different periods is not represented by different tags. The period is represented by the date context applied to an item (current year and previous year). For example the same tag is used for operating profit for 2009 as for 2008. Similarly values at the beginning and end of periods are distinguished by date – not by tag. (The taxonomy contains some tags with labels ending '…start of period' and '…end of period'. This is purely to aid presentation and help users identify tags. These start/end labels reference the same underlying tag.)

The rest of this section provides guidance and rules on the tagging of reports. The following section provides guidance and rules on the entry of data values.

The rules stated below refer to tag in the singular but they must also be taken to mean combinations of tags covering both the line item tag and associated dimensional tags where appropriate.


Choice of tag


A data item MUST be matched against the closest available tag in the appropriate taxonomy based on the tag's label position in the presentation view accounting reference data type and period type PROVIDED that the use of the element to represent the data item does not introduce a material distortion in the meaning of the business report.

In general the appropriate tag for a data item should be relatively obvious once the tag is located in the taxonomy. For example an item in the profit and loss statement described by a company as 'Profit prior to tax' and appearing prior to the tax charge on ordinary activities can obviously be matched against an element in that position in the UK GAAP taxonomy labelled 'Profit (loss) on ordinary activities before tax'. Clearly the label used for an item in the taxonomy may not exactly match the description used by a company.

The position of a tag in the taxonomy is a strong clue to meaning: for example a tag listed in the taxonomy under 'Operating costs' is obviously an expense item and not an asset.

However a tag's position in a presentation view will not necessarily match that of the corresponding item in a company's report. Companies vary significantly in where they choose to place items in their reports. The presentation view in the taxonomy provides guidance on meaning but it is NOT definitional. For example tags from the primary statements sectionmay be used for line items in the notes of a company report and vice versa. Companies may thus find suitable tags in locations which do not match the particular presentation of their accounts.

Companies may use differing terminology for the same accounting concept. Preparers must not be distracted by terminology and should identify the real meaning of items and tag accordingly.

The basic rule on matching allows some latitude in the application of tags to line items in reports. It seeks a best available match. It recognises that the limited number of tags in the taxonomy cannot represent all the subtlety of meaning which a company may impart through the descriptions and details of formatting which it employs in its financial statements. The latter may be reproduced using Inline XBRL while tagging is used to convey the general meaning of the item concerned.

Nevertheless tags should not be 'stretched' in their meaning in order to tag a data item. This would undermine the consistency of tagging across companies.

It is the responsibility of the reporting organisation to make a reasonable judgement on the application of tags in its financial reports.


Scope of tagging


Tags are expected to be applied to the financial sections of reports. Data in the Directors' and Auditors' Report is only expected to be tagged if specific tags exist for this data within the Directors' and Auditors' Report sections of the taxonomy. Other textual reports such as Chairman's Statement Financial Review and the like if they exist are NOT expected to be tagged.

For example information on turnover or profit in the Directors' Report need not be tagged since it is assumed this data will be tagged in the financial section of the report. However information on directors' remuneration may only appear in the Directors' Report and must then be tagged there. Tags for this data exist in the Directors' Report section of the taxonomy.


Significant numeric data


Significant numeric data presented within text in the financial section of a report MUST be tagged with the appropriate numeric tags for that data. It MUST NOT be hidden within a text tag or within an XBRL footnote.

This rule reflects the fact that numeric data may be hidden from analysis software by tagging it as text or dropping it within a footnote. The choice between reporting numeric data as a line item or placing it in a footnote may not be important to a human reader but it is important when data is encoded in XBRL. Note that this rule is not concerned about how data is displayed in a human–readable presentation – purely about how it is tagged.

Where appropriate tags exist for a section of text and numeric data within the text then both the text and the numeric data MUST be tagged.


No tag available


If no tag in the taxonomy provides a suitable match for a particular data item the item may be left as an untagged text line.


Alternative tags


When alternative tags of different levels of granularity in the taxonomy match a data item in the accounts preparers MUST choose the tag which best represents the intended meaning and level of granularity of the data item. In doing so they MUST abide by the following rules:

  1. If the data item is intended to represent a broad total then the tag which represents such a total MUST be used. In particular broad total tags should be used to represent data in primary statements of accounts.
  2. If the data item is intended to represent a detailed breakdown then the tag which represents that level of breakdown MUST be used. In general detailed or granular tags should be used to represent data presented in notes to the accounts.

Alternative tags with different degrees of generality will often be available to match an item in a business report. The positioning of the tags within the taxonomy – and thus the level of detail they are intended to represent – will indicate which should be used.


For example a company may report 'bank interest receivable' in its profit and loss statement. This must be matched against the tag 'Other interest receivable and similar income' in the profit and loss statement section of the taxonomy. It must not be matched against the tag for 'Interest receivable on bank deposits' buried within a breakdown of types of interest receivable in the notes section of the taxonomy. (Clearly if no other types of interest are received the two items will have the same value but the aim of this rule is to ensure that tags representing broad totals are used consistently by different organisations. The alternative tags concerned will often have different accounting references.) Failure to follow this rule will mean that tags for expected totals will be missing.


By contrast for example a company may report 'bank overdrafts' in a note showing a detailed breakdown of liabilities. The taxonomy may contain tags for such a breakdown representing (a) 'bank borrowings and overdrafts' (b) 'bank borrowings' and (c) 'bank overdrafts'. If the company does not have any bank loans it may appear that the company line item can be matched against either (a) or (c). In this case however the data item must be matched against (c) – the tag in the breakdown which specifically matches the meaning and level of granularity of the line item.

Similarly a company may report 'corporation tax paid' as the sole tax related item in its cash flow statement. This must be matched against the tag 'Taxation expense (credit)' shown in the taxonomy cash flow statement. The tag 'UK corporation tax paid' exists to tag such an item when it appears as part of a detailed breakdown in the notes to cash flow alongside other tax payments and receipts.


Unique application of tags


Apart from in the special case of tuples the value assigned to each tag for a single context in an XBRL report MUST be unique. The same tag MUST NOT be assigned to different data values with the same context.

The context of an item means the period entity and dimensions to which it applies.

This rule means that the same tag must not be used for different data in the same report. For example if the 'Operating profit (loss)' tag is attached to a value of £1 million for the financial year 2008 it must not also be attached to a value £1.5 million for the same period and company.

This rule ensures the consistency of reports from the point of view of both accounting and tagging and if not followed will result in an error being return from the Government Gateway whilst attempting to file.

Clearly the same tag may be reused for different time periods and for different dimensions such as continuing operations joint–ventures and the like.


Repetition of tags within tuples


Tags within tuples may be used multiple times for the same context within an XBRL report but in this case they must be reported in different occurrences of the tuple.

This rule reflects the normal functionality of tuples.


Tagging of multiple occurrences of data items


If the same data item appears in different places in a financial section of a report then all occurrencesof that data item must be tagged even if different scaling applies to some occurrences. This rule ensures that data is consistently reported in XBRL and discrepancies between human readable andXBRL reports do not occur.


For example the same accounting line item may appear both in a primary statement and in a note to the accounts. Both occurrences must be tagged.


This rule ensures that data in financial reports is filed consistently and enables a range of basic validity checks. It helps to ensure that different numbers for the same thing do not appear in different places within a report. It is important among other things for assurance on accounts.

This rule concerns the financial section of accounts not the textual reports which precede the financial section.


Use of 'generic' tags


A small number of dimensions contain 'generic members' to represent expected breakdowns of information. For example the 'Entity officers' dimension includes Director 1 Director 2 etc. as well as Chairman Chief executive and the like.

Other dimensions with generic members include:

  • Acquisitions: Acquisition 1 Acquisition 2 etc.
  • Joint–Ventures Associates and Subsidiaries: Associate 1 Associate 2 etc.
  • Business and operating segments: Business segment 1 Business segment 2 etc.
  • Pension schemes:Pension scheme 1 Pension scheme 2 etc.

The identification of dimensions with generic members should be obvious. In case of any doubt these are dimensions whose members have a sequence of numbers after their names.

All of these dimensions are attached to a name and / or description tag so that the identity of a particular dimension member may be defined.

For example there is a 'Name of entity officer' tag which is linked to the 'Entity officers' dimension. Similarly there is a 'Name of defined benefit scheme' tag which is linked to the 'Pension schemes' dimension.

The following rules apply to the use of generic dimension members.

When a generic dimension tag is used in an XBRL report the associated name and/or description tag MUST be used in combination with that tag to provide a human readable identification.

For example generic dimension tags like Director 1 Director 2 Acquisition 1 Acquisition 2 must be identified using the appropriate name tag in combination with them.

Generic dimension tags MUST be used consistently within a report. Any data tagged with a particular generic dimension tag MUST relate uniquely to that single dimension tag.

For example if Director 1 has been identified as Joe Bloggs then the Director 1 dimension tag must be used consistently throughout a report to apply only to data related to Joe Bloggs. A single generic dimension tag must not be used to identify different things within a single report.

The number of generic tags defined in each dimension should be more than sufficient for most purposes. For example the 'Entity officers' dimension allows up to 80 directors to be identified since each of the 40 generic tags for director may be separately identified as either executive or non–executive.

In the very rare cases where the number of generic dimension tags is insufficient preparers may use text in Inline XBRL to report the data which cannot be tagged.


Use of 'fixed value' tags


A small number of tags have a predefined fixed value of 'nil'. They have their effect simply by being included in an XBRL report in combination with an appropriate dimension tag. They do not contain any value in the XBRL report.

An example is 'Country of formation or incorporation'. To represent country of incorporation this tag should be included in an XBRL report in combination with the appropriate dimension tag from the 'Countries' dimension. This ensures unambiguous identification of the country concerned.

Another example is 'Director signing report' in the Directors' Report section. This tag should appear in combination with the dimension tag identifying the director concerned from the 'Entity officers' dimension. (The name of the director is defined separately by the 'Name of entity officer' tag used in combination with dimension tag for the director.)


Use of 'free–text comment' tags


Free–text comment tags MUST only be used to cover supplementary comment in the specific area to which they apply. They MUST NOT substitute for specific tags where the latter would be appropriate.

For examplefree–text comment tags should be used to tag the general explanation which might appear at the bottom of a note to the accounts for which no other suitable tag exists.


Use of tags for 'Other…' data


A number of tags represent a residual amount from a list of items. An example is 'Other creditors'.

These 'Other' tags may be used to tag items which are genuinely labelled as other / residual in a company report or they may be used to tag a single remaining item in a list for which no other suitable tag exists. However a single other tag MUST NOT be used to tag multiple different items for the same period. This would break above on the unique application of tags. If multiple items exist for which no tag is available they may simply be reported as text with no tagging.


Compulsory tags


The following tags MUST be used in XBRL accounts to aid in processing:

  1. Entity current legal or registered name
  2. Companies House registered number (where applicable)
  3. Company dormant / not dormant
  4. Company trading / not trading
  5. Start date for period covered by report
  6. End date for period covered by report
  7. Directors report date of signing
  8. Directors signing directors report
  9. Balance sheet date
  10. Balance sheet date of approval
  11. Balance sheet approving directors / authority
  12. All declarations under 'Statements in Directors' Report' and 'Directors' or entity's declarations' which apply to the entity concerned.

The rules on the directors' report apply to the equivalent of this report in organisations which do not publish a directors' report. For example they apply to the trustees' report provided by charities.


Tagging of comparative data


In general comparative data for preceding periods in financial reports MUST be tagged just as data for the most recent period is tagged. This rule includes previous period data for which no current data is published. However HMRC is NOT asking for previous year comparatives in the first year of mandatory filing for the purposes of accounts included as part of the CT600 return.

The exception to the general rule for the first year of mandatory filing to HMRC from 31 March 2011 to 31 March 2012 reflects the fact that mandatory tagging did not apply prior to 31 March 2011. Preparers are still encouraged to provide tagging of comparatives but it is not mandatory to do so.


Distinction of company and group data


The dimension tags 'Consolidated' and 'Company [default]' exist to distinguish group and company data. Their use will normally be straightforward with company being the default. In some cases however an organisation may present some data in its accounts as applying to both group and company. For example such combined accounts may show separate balance sheets for the group and the company but a single table for tangible assets with the same tangible asset values applying to both group and company. The general rule for handling such cases in Inline XBRL is:

When group and company data in a financial report is being tagged a data item which represents a value for both the company and the group MUST be tagged twice: once using the appropriate 'Consolidated' dimensional tag to identify the data as pertaining to the group and once without a tag for consolidation indicating that it pertains to the 'Company [default]'. Clearly other tags attached to the data item will be identical.

This double tagging is necessary to identify the correct meaning of the data to software.

Note however that up to 31 March 2013 HMRC has said that tagging of group data is NOT mandatory. Preparers may file group data in ordinary text format without tagging.


'Not applicable' tag


A special tag 'Not applicable' is defined as a dimension member in a number of dimensions. When included it is always the default tag in the dimension. Its full label is 'Not applicable [default]'.

This tag automatically causes the dimension concerned to be ignored except when a preparer actively uses a tag from the dimension. It exists for technical reasons and simplifies the design of dimensions and the work of tagging.

Accounts preparers should never need to use this tag when tagging data and effectively can ignore it.


Positive and negative values


The correct positive and negative sign must be applied to data values in an XBRL report. This sign is determined by XBRL rules based on the taxonomy. It is NOT necessarily the same as the sign which is used in the human–readable view of a report. The latter is controlled by the preparer and will depend on the particular conventions which a company follows. (Signs can be transformed between the underlying XBRL data value and the human–readable presentation using features of Inline XBRL.)

Preparers of XBRL reports MUST follow the rules below when entering XBRL data values:

  1. Data MUST always be entered as positive UNLESS rule (b) below requires otherwise.
  2. Where data may be positive or negative the label will indicate the correct sign of the item. Labels will use brackets around terms to show what data should be entered as negative.

Examples of sign indicators in labels are:

  • Operating profit (loss)
  • Net current assets (liabilities)
  • Net cash flow (outflow) from financing
  • Funds (debts) acquired with subsidiaries

If a company reports an operating profit it will thus enter the value of the profit as positive. On the other hand if it reports a loss it will enter the value of the loss as negative. Similarly it will enter funds acquired with subsidiaries as positive but debts acquired as a negative value.

The taxonomy also allocates debit / credit balance indicators to some monetary tags. These may help guide userson the correct sign but they only sensibly apply to income and asset / liability data and the wording of labels always takes precedence in determining sign.


Tagging of text


A large range of tags of string data type are available for tagging of text. These range from tags for simple text such as entity name through to longer declarations or descriptions such as tags for accounting policies. Dimension tags may apply to text tags in exactly the same way as numeric tags. For example the policy on a particular class of tangible assets may be identified by combining the 'Tangible fixed assets policy' tag with the appropriate dimension tag for that class.

Any text including paragraphs numbers and other formatting may be tagged with a text tag. However preparers should note the rule above on not burying significant numeric data within a text tag. Where it is necessary to tag a section of text which includes numeric data for which a tag is available preparers must tag the numeric data as well as the section of text concerned.

Preparers must make a reasonable judgement on precisely what portion of a particular textual statement should carry a tag. In most cases this should be obvious. The granularity of text string tags has been defined as far as practical to accord with likely company textual statements.


XBRL Concepts



Taxonomies are at the heart of XBRL they define the individual tags that identify specific items of business data.

The taxonomy used within Compac is UK GAAP; this represents typical reporting by companies under UK GAAP including FRSSE regulations. A special extension to the UK GAAP taxonomy exists for charities.

The UK GAAP taxonomy contains a number of common components including modules covering the Directors’ Report Auditors Report and standard business data.It also includes information on HMRC minimum tagging requirements.

XBRL UK are responsible for the maintenance of the taxonomy; the tags within Compac are made available exactly as they are supplied by XBRL UK. Over time it is expected the taxonomy will be expanded to cover items which may be reasonably commonly used but are missing now. The taxonomy will also be amendedto improve its accuracy clarity and ease of use.

Comments and questions on the UK GAAP taxonomy and use of XBRL are welcome. Let us know by emailing


Taxonomy features and content

The taxonomy includes a range of features to identify tags to aid ease of use and to enable software to process XBRL data efficiently.  It also contains special features to cope with different aspects and formats of reporting. The main features are:




The human-readable labels on tags provide their main definition – as far as possible they uniquely identify the tag concerned.  Labels in taxonomies are typically longer and more explicit than descriptions of line items in financial reports.  For example a taxonomy label will say ‘Tax on profit or loss on ordinary activities’ not just ‘Tax’. 




The UK GAAP taxonomy is presented in the same format as the financial reports thus mimicking the basic structure of accounts with primary statements followed by notes and detailed disclosures. 

The position of a tag in the presentation hierarchy of the taxonomy should give a strong indication of its use and meaning.  For example ‘Tax on profit or loss on ordinary activities’ will appear in the profit & loss section of the taxonomy between profit before tax and profit after tax.  Some tags may appear in multiple places in the presentation view because they may typically be reported in different positions in accounts.

The presentation of the taxonomy is a ‘common denominator view’ which mimics the typical positioning of items in accounts.  It is intended purely to help users locate and identify tags in the taxonomy.  It does not determine how items are presented in accounts filed in Inline XBRL – that is determined entirely independently by the preparer.  Nor does it represent how data may be aggregated.  For example some items located within notes in the taxonomy may well be included in primary statements in some company accounts or vice versa. 

Taxonomy presentation views do not attempt to represent all possible layouts of accounts.  Given the huge variation