Some long bit of markdown that you want to be able to collapse (e.g. a long log file).
Use:
<details>
<summary>Section title</summary>
The long details to hide
</details>
Example
2018-03-27 20:20:08.84 Server Setup step is copying system data file 'C:\templatedata\master.mdf' to '/var/opt/mssql/data/master.mdf'.
2018-03-27 20:20:08.90 Server Did not find an existing master data file /var/opt/mssql/data/master.mdf, copying the missing default master and other system database files. If you have moved the database location, but not moved the database files, startup may fail. To repair: shutdown SQL Server, move the master database to configured location, and restart.
2018-03-27 20:20:08.90 Server Setup step is copying system data file 'C:\templatedata\mastlog.ldf' to '/var/opt/mssql/data/mastlog.ldf'.
2018-03-27 20:20:08.91 Server Setup step is copying system data file 'C:\templatedata\model.mdf' to '/var/opt/mssql/data/model.mdf'.
2018-03-27 20:20:08.92 Server Setup step is copying system data file 'C:\templatedata\modellog.ldf' to '/var/opt/mssql/data/modellog.ldf'.
2018-03-27 20:20:08.94 Server Setup step is copying system data file 'C:\templatedata\msdbdata.mdf' to '/var/opt/mssql/data/msdbdata.mdf'.
2018-03-27 20:20:08.95 Server Setup step is copying system data file 'C:\templatedata\msdblog.ldf' to '/var/opt/mssql/data/msdblog.ldf'.
2018-03-27 20:20:09.05 Server Microsoft SQL Server 2017 (RTM-CU5) (KB4092643) - 14.0.3023.8 (X64)
Mar 2 2018 18:24:44
Copyright (C) 2017 Microsoft Corporation
Developer Edition (64-bit) on Linux (Ubuntu 16.04.4 LTS)
2018-03-27 20:20:09.05 Server UTC adjustment: 0:00
2018-03-27 20:20:09.05 Server (c) Microsoft Corporation.
2018-03-27 20:20:09.05 Server All rights reserved.
2018-03-27 20:20:09.05 Server Server process ID is 4120.
2018-03-27 20:20:09.06 Server Logging SQL Server messages in file '/var/opt/mssql/log/errorlog'.
2018-03-27 20:20:09.06 Server Registry startup parameters:
-d /var/opt/mssql/data/master.mdf
-l /var/opt/mssql/data/mastlog.ldf
-e /var/opt/mssql/log/errorlog
2018-03-27 20:20:09.16 Server SQL Server detected 1 sockets with 2 cores per socket and 2 logical processors per socket, 2 total logical processors; using 2 logical processors based on SQL Server licensing. This is an informational message; no user action is required.
2018-03-27 20:20:09.16 Server SQL Server is starting at normal priority base (=7). This is an informational message only. No user action is required.
2018-03-27 20:20:09.16 Server Detected 3143 MB of RAM. This is an informational message; no user action is required.
2018-03-27 20:20:09.16 Server Using conventional memory in the memory manager.
2018-03-27 20:20:09.38 Server Buffer pool extension is already disabled. No action is necessary.
2018-03-27 20:20:09.60 Server InitializeExternalUserGroupSid failed. Implied authentication will be disabled.
2018-03-27 20:20:09.60 Server Implied authentication manager initialization failed. Implied authentication will be disabled.
2018-03-27 20:20:09.61 Server Successfully initialized the TLS configuration. Allowed TLS protocol versions are ['1.0 1.1 1.2']. Allowed TLS ciphers are ['ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-ECDSA-AES128-SHA:AES256-GCM-SHA384:AES128-GCM-SHA256:AES256-SHA256:AES128-SHA256:AES256-SHA:AES128-SHA:!DHE-RSA-AES256-GCM-SHA384:!DHE-RSA-AES128-GCM-SHA256:!DHE-RSA-AES256-SHA:!DHE-RSA-AES128-SHA'].
2018-03-27 20:20:09.65 Server The maximum number of dedicated administrator connections for this instance is '1'
2018-03-27 20:20:09.65 Server Node configuration: node 0: CPU mask: 0x0000000000000003:0 Active CPU mask: 0x0000000000000003:0. This message provides a description of the NUMA configuration for this computer. This is an informational message only. No user action is required.
2018-03-27 20:20:09.68 Server Using dynamic lock allocation. Initial allocation of 2500 Lock blocks and 5000 Lock Owner blocks per node. This is an informational message only. No user action is required.
2018-03-27 20:20:09.69 Server In-Memory OLTP initialized on lowend machine.
2018-03-27 20:20:09.88 Server Database Instant File Initialization: enabled. For security and performance considerations see the topic 'Database Instant File Initialization' in SQL Server Books Online. This is an informational message only. No user action is required.
2018-03-27 20:20:09.90 Server Query Store settings initialized with enabled = 1,
2018-03-27 20:20:09.91 spid6s Starting up database 'master'.
2018-03-27 20:20:09.92 Server Software Usage Metrics is disabled.
2018-03-27 20:20:10.11 spid6s The tail of the log for database master is being rewritten to match the new sector size of 4096 bytes. 3072 bytes at offset 418816 in file /var/opt/mssql/data/mastlog.ldf will be written.
2018-03-27 20:20:10.27 spid6s Converting database 'master' from version 862 to the current version 869.
2018-03-27 20:20:10.27 spid6s Database 'master' running the upgrade step from version 862 to version 863.
2018-03-27 20:20:10.30 spid6s Database 'master' running the upgrade step from version 863 to version 864.
2018-03-27 20:20:10.33 spid6s Database 'master' running the upgrade step from version 864 to version 865.
2018-03-27 20:20:10.34 spid6s Database 'master' running the upgrade step from version 865 to version 866.
2018-03-27 20:20:10.34 spid6s Database 'master' running the upgrade step from version 866 to version 867.
2018-03-27 20:20:10.35 spid6s Database 'master' running the upgrade step from version 867 to version 868.
2018-03-27 20:20:10.36 spid6s Database 'master' running the upgrade step from version 868 to version 869.
2018-03-27 20:20:10.61 spid6s Resource governor reconfiguration succeeded.
2018-03-27 20:20:10.61 spid6s SQL Server Audit is starting the audits. This is an informational message. No user action is required.
2018-03-27 20:20:10.62 spid6s SQL Server Audit has started the audits. This is an informational message. No user action is required.
2018-03-27 20:20:10.68 spid6s SQL Trace ID 1 was started by login "sa".
2018-03-27 20:20:10.72 spid18s Password policy update was successful.
2018-03-27 20:20:10.74 spid6s Server name is '1bf66e8c4644'. This is an informational message only. No user action is required.
2018-03-27 20:20:10.77 spid22s Always On: The availability replica manager is starting. This is an informational message only. No user action is required.
2018-03-27 20:20:10.77 spid6s Starting up database 'msdb'.
2018-03-27 20:20:10.78 spid9s Starting up database 'mssqlsystemresource'.
2018-03-27 20:20:10.78 spid22s Always On: The availability replica manager is waiting for the instance of SQL Server to allow client connections. This is an informational message only. No user action is required.
2018-03-27 20:20:10.80 spid9s The resource database build version is 14.00.3023. This is an informational message only. No user action is required.
2018-03-27 20:20:10.84 spid9s Starting up database 'model'.
2018-03-27 20:20:11.16 spid9s The tail of the log for database model is being rewritten to match the new sector size of 4096 bytes. 2048 bytes at offset 75776 in file /var/opt/mssql/data/modellog.ldf will be written.
2018-03-27 20:20:11.21 spid18s A self-generated certificate was successfully loaded for encryption.
2018-03-27 20:20:11.21 spid9s Converting database 'model' from version 862 to the current version 869.
2018-03-27 20:20:11.21 spid18s Server is listening on [ 'any' <ipv4> 1433].
2018-03-27 20:20:11.22 spid9s Database 'model' running the upgrade step from version 862 to version 863.
2018-03-27 20:20:11.24 Server Server is listening on [ 127.0.0.1 <ipv4> 1434].
2018-03-27 20:20:11.24 Server Dedicated admin connection support was established for listening locally on port 1434.
2018-03-27 20:20:11.26 spid18s SQL Server is now ready for client connections. This is an informational message; no user action is required.
2018-03-27 20:20:11.26 spid9s Database 'model' running the upgrade step from version 863 to version 864.
2018-03-27 20:20:11.28 spid9s Database 'model' running the upgrade step from version 864 to version 865.
2018-03-27 20:20:11.28 spid6s The tail of the log for database msdb is being rewritten to match the new sector size of 4096 bytes. 512 bytes at offset 52736 in file /var/opt/mssql/data/MSDBLog.ldf will be written.
2018-03-27 20:20:11.29 spid9s Database 'model' running the upgrade step from version 865 to version 866.
2018-03-27 20:20:11.29 spid9s Database 'model' running the upgrade step from version 866 to version 867.
2018-03-27 20:20:11.30 spid9s Database 'model' running the upgrade step from version 867 to version 868.
2018-03-27 20:20:11.31 spid6s Converting database 'msdb' from version 862 to the current version 869.
2018-03-27 20:20:11.31 spid6s Database 'msdb' running the upgrade step from version 862 to version 863.
2018-03-27 20:20:11.32 spid9s Database 'model' running the upgrade step from version 868 to version 869.
2018-03-27 20:20:11.34 spid6s Database 'msdb' running the upgrade step from version 863 to version 864.
2018-03-27 20:20:11.35 spid6s Database 'msdb' running the upgrade step from version 864 to version 865.
2018-03-27 20:20:11.35 spid6s Database 'msdb' running the upgrade step from version 865 to version 866.
2018-03-27 20:20:11.35 spid6s Database 'msdb' running the upgrade step from version 866 to version 867.
2018-03-27 20:20:11.36 spid6s Database 'msdb' running the upgrade step from version 867 to version 868.
2018-03-27 20:20:11.36 spid6s Database 'msdb' running the upgrade step from version 868 to version 869.
2018-03-27 20:20:11.42 spid9s Polybase feature disabled.
2018-03-27 20:20:11.43 spid9s Clearing tempdb database.
2018-03-27 20:20:12.03 spid9s Starting up database 'tempdb'.
2018-03-27 20:20:12.30 spid9s The tempdb database has 1 data file(s).
2018-03-27 20:20:12.31 spid24s The Service Broker endpoint is in disabled or stopped state.
2018-03-27 20:20:12.32 spid24s The Database Mirroring endpoint is in disabled or stopped state.
2018-03-27 20:20:12.33 spid24s Service Broker manager has started.
2018-03-27 20:20:12.45 spid6s Recovery is complete. This is an informational message only. No user action is required.
2018-03-27 20:20:12.47 spid22s The default language (LCID 0) has been set for engine and full-text services.
2018-03-27 20:20:12.80 spid51 Configuration option 'show advanced options' changed from 0 to 1. Run the RECONFIGURE statement to install.
2018-03-27 20:20:12.84 spid51 Configuration option 'Agent XPs' changed from 0 to 1. Run the RECONFIGURE statement to install.
2018-03-27 20:20:12.84 spid51 Configuration option 'show advanced options' changed from 1 to 0. Run the RECONFIGURE statement to install.
2018-03-27 20:20:13.02 spid51 Attempting to load library 'xpsqlbot.dll' into memory. This is an informational message only. No user action is required.
2018-03-27 20:20:13.03 spid51 Using 'xpsqlbot.dll' version '2017.140.3023' to execute extended stored procedure 'xp_qv'. This is an informational message only; no user action is required.
2018-03-27 20:20:13.13 spid51 Attempting to load library 'xpstar.dll' into memory. This is an informational message only. No user action is required.
2018-03-27 20:20:13.20 spid51 Using 'xpstar.dll' version '2017.140.3023' to execute extended stored procedure 'xp_sqlagent_notify'. This is an informational message only; no user action is required.
2018-03-27 20:25:17.76 spid53 Using 'dbghelp.dll' version '4.0.5'
2018-03-27 20:25:21.30 spid53 Attempting to load library 'xplog70.dll' into memory. This is an informational message only. No user action is required.
2018-03-27 20:25:21.44 spid53 Using 'xplog70.dll' version '2017.140.3023' to execute extended stored procedure 'xp_msver'. This is an informational message only; no user action is required.